cp's OEIS Frontend

A000108 Catalan numbers: C(n) = binomial(2n,n)/(n+1) = (2n)!/(n!(n+1)!).

%I A000108 M1459 N0577 #2121 Aug 20 2025 10:54:28
%S A000108 1,1,2,5,14,42,132,429,1430,4862,16796,58786,208012,742900,2674440,
%T A000108 9694845,35357670,129644790,477638700,1767263190,6564120420,
%U A000108 24466267020,91482563640,343059613650,1289904147324,4861946401452,18367353072152,69533550916004,263747951750360,1002242216651368,3814986502092304
%N A000108 Catalan numbers: C(n) = binomial(2n,n)/(n+1) = (2n)!/(n!(n+1)!).
%C A000108 These were formerly sometimes called Segner numbers.
%C A000108 A very large number of combinatorial interpretations are known - see references, esp. R. P. Stanley, "Catalan Numbers", Cambridge University Press, 2015. This is probably the longest entry in the OEIS, and rightly so.
%C A000108 The solution to Schröder's first problem: number of ways to insert n pairs of parentheses in a word of n+1 letters. E.g., for n=2 there are 2 ways: ((ab)c) or (a(bc)); for n=3 there are 5 ways: ((ab)(cd)), (((ab)c)d), ((a(bc))d), (a((bc)d)), (a(b(cd))).
%C A000108 Consider all the binomial(2n,n) paths on squared paper that (i) start at (0, 0), (ii) end at (2n, 0) and (iii) at each step, either make a (+1,+1) step or a (+1,-1) step. Then the number of such paths that never go below the x-axis (Dyck paths) is C(n). [Chung-Feller]
%C A000108 Number of noncrossing partitions of the n-set. For example, of the 15 set partitions of the 4-set, only [{13},{24}] is crossing, so there are a(4)=14 noncrossing partitions of 4 elements. - _Joerg Arndt_, Jul 11 2011
%C A000108 Noncrossing partitions are partitions of genus 0. - _Robert Coquereaux_, Feb 13 2024
%C A000108 a(n-1) is the number of ways of expressing an n-cycle (123...n) in the symmetric group S_n as a product of n-1 transpositions (u_1,v_1)*(u_2,v_2)*...*(u_{n-1},v_{n-1}) where u_i<v_i and u_k <= u_j for k < j; see example.  If the condition is dropped, one obtains A000272. - _Joerg Arndt_ and Greg Stevenson, Jul 11 2011
%C A000108 a(n) is the number of ordered rooted trees with n nodes, not including the root. See the Conway-Guy reference where these rooted ordered trees are called plane bushes. See also the Bergeron et al. reference, Example 4, p. 167. - _Wolfdieter Lang_, Aug 07 2007
%C A000108 As shown in the paper from Beineke and Pippert (1971), a(n-2)=D(n) is the number of labeled dissections of a disk, related to the number R(n)=A001761(n-2) of labeled planar 2-trees having n vertices and rooted at a given exterior edge, by the formula D(n)=R(n)/(n-2)!. - _M. F. Hasler_, Feb 22 2012
%C A000108 Shifts one place left when convolved with itself.
%C A000108 For n >= 1, a(n) is also the number of rooted bicolored unicellular maps of genus 0 on n edges. - Ahmed Fares (ahmedfares(AT)my-deja.com), Aug 15 2001
%C A000108 Number of ways of joining 2n points on a circle to form n nonintersecting chords. (If no such restriction imposed, then the number of ways of forming n chords is given by (2n-1)!! = (2n)!/(n!*2^n) = A001147(n).)
%C A000108 Arises in Schubert calculus - see Sottile reference.
%C A000108 Inverse Euler transform of sequence is A022553.
%C A000108 With interpolated zeros, the inverse binomial transform of the Motzkin numbers A001006. - _Paul Barry_, Jul 18 2003
%C A000108 The Hankel transforms of this sequence or of this sequence with the first term omitted give A000012 = 1, 1, 1, 1, 1, 1, ...; example: Det([1, 1, 2, 5; 1, 2, 5, 14; 2, 5, 14, 42; 5, 14, 42, 132]) = 1 and Det([1, 2, 5, 14; 2, 5, 14, 42; 5, 14, 42, 132; 14, 42, 132, 429]) = 1. - _Philippe Deléham_, Mar 04 2004
%C A000108 a(n) equals the sum of squares of terms in row n of triangle A053121, which is formed from successive self-convolutions of the Catalan sequence. - _Paul D. Hanna_, Apr 23 2005
%C A000108 Also coefficients of the Mandelbrot polynomial M iterated an infinite number of times. Examples: M(0) = 0 = 0*c^0 = [0], M(1) = c = c^1 + 0*c^0 = [1 0], M(2) = c^2 + c = c^2 + c^1 + 0*c^0 = [1 1 0], M(3) = (c^2 + c)^2 + c = [0 1 1 2 1], ... ... M(5) = [0 1 1 2 5 14 26 44 69 94 114 116 94 60 28 8 1], ... - Donald D. Cross (cosinekitty(AT)hotmail.com), Feb 04 2005
%C A000108 The multiplicity with which a prime p divides C_n can be determined by first expressing n+1 in base p. For p=2, the multiplicity is the number of 1 digits minus 1. For p an odd prime, count all digits greater than (p+1)/2; also count digits equal to (p+1)/2 unless final; and count digits equal to (p-1)/2 if not final and the next digit is counted. For example, n=62, n+1 = 223_5, so C_62 is not divisible by 5. n=63, n+1 = 224_5, so 5^3 | C_63. - _Franklin T. Adams-Watters_, Feb 08 2006
%C A000108 Koshy and Salmassi give an elementary proof that the only prime Catalan numbers are a(2) = 2 and a(3) = 5. Is the only semiprime Catalan number a(4) = 14? - _Jonathan Vos Post_, Mar 06 2006
%C A000108 The answer is yes. Using the formula C_n = binomial(2n,n)/(n+1), it is immediately clear that C_n can have no prime factor greater than 2n. For n >= 7, C_n > (2n)^2, so it cannot be a semiprime. Given that the Catalan numbers grow exponentially, the above consideration implies that the number of prime divisors of C_n, counted with multiplicity, must grow without limit. The number of distinct prime divisors must also grow without limit, but this is more difficult. Any prime between n+1 and 2n (exclusive) must divide C_n. That the number of such primes grows without limit follows from the prime number theorem. - _Franklin T. Adams-Watters_, Apr 14 2006
%C A000108 The number of ways to place n indistinguishable balls in n numbered boxes B1,...,Bn such that at most a total of k balls are placed in boxes B1,...,Bk for k=1,...,n. For example, a(3)=5 since there are 5 ways to distribute 3 balls among 3 boxes such that (i) box 1 gets at most 1 ball and (ii) box 1 and box 2 together get at most 2 balls:(O)(O)(O), (O)()(OO), ()(OO)(O), ()(O)(OO), ()()(OOO). - _Dennis P. Walsh_, Dec 04 2006
%C A000108 a(n) is also the order of the semigroup of order-decreasing and order-preserving full transformations (of an n-element chain) - now known as the Catalan monoid. - _Abdullahi Umar_, Aug 25 2008
%C A000108 a(n) is the number of trivial representations in the direct product of 2n spinor (the smallest) representations of the group SU(2) (A(1)). - Rutger Boels (boels(AT)nbi.dk), Aug 26 2008
%C A000108 The invert transform appears to converge to the Catalan numbers when applied infinitely many times to any starting sequence. - _Mats Granvik_, _Gary W. Adamson_ and _Roger L. Bagula_, Sep 09 2008, Sep 12 2008
%C A000108 Limit_{n->oo} a(n)/a(n-1) = 4. - Francesco Antoni (francesco_antoni(AT)yahoo.com), Nov 24 2008
%C A000108 Starting with offset 1 = row sums of triangle A154559. - _Gary W. Adamson_, Jan 11 2009
%C A000108 C(n) is the degree of the Grassmannian G(1,n+1): the set of lines in (n+1)-dimensional projective space, or the set of planes through the origin in (n+2)-dimensional affine space. The Grassmannian is considered a subset of N-dimensional projective space, N = binomial(n+2,2) - 1. If we choose 2n general (n-1)-planes in projective (n+1)-space, then there are C(n) lines that meet all of them. - Benji Fisher (benji(AT)FisherFam.org), Mar 05 2009
%C A000108 Starting with offset 1 = A068875: (1, 2, 4, 10, 18, 84, ...) convolved with Fine numbers, A000957: (1, 0, 1, 2, 6, 18, ...). a(6) = 132 = (1, 2, 4, 10, 28, 84) dot (18, 6, 2, 1, 0, 1) = (18 + 12 + 8 + 10 + 0 + 84) = 132. - _Gary W. Adamson_, May 01 2009
%C A000108 Convolved with A032443: (1, 3, 11, 42, 163, ...) = powers of 4, A000302: (1, 4, 16, ...). - _Gary W. Adamson_, May 15 2009
%C A000108 Sum_{k>=1} C(k-1)/2^(2k-1) = 1. The k-th term in the summation is the probability that a random walk on the integers (beginning at the origin) will arrive at positive one (for the first time) in exactly (2k-1) steps. - _Geoffrey Critzer_, Sep 12 2009
%C A000108 C(p+q)-C(p)*C(q) = Sum_{i=0..p-1, j=0..q-1} C(i)*C(j)*C(p+q-i-j-1). - _Groux Roland_, Nov 13 2009
%C A000108 Leonhard Euler used the formula C(n) = Product_{i=3..n} (4*i-10)/(i-1) in his 'Betrachtungen, auf wie vielerley Arten ein gegebenes polygonum durch Diagonallinien in triangula zerschnitten werden könne' and computes by recursion C(n+2) for n = 1..8. (Berlin, 4th September 1751, in a letter to Goldbach.) - _Peter Luschny_, Mar 13 2010
%C A000108 Let A179277 = A(x). Then C(x) is satisfied by A(x)/A(x^2). - _Gary W. Adamson_, Jul 07 2010
%C A000108 a(n) is also the number of quivers in the mutation class of type B_n or of type C_n. - _Christian Stump_, Nov 02 2010
%C A000108 From _Matthew Vandermast_, Nov 22 2010: (Start)
%C A000108 Consider a set of A000217(n) balls of n colors in which, for each integer k = 1 to n, exactly one color appears in the set a total of k times. (Each ball has exactly one color and is indistinguishable from other balls of the same color.) a(n+1) equals the number of ways to choose 0 or more balls of each color while satisfying the following conditions: 1. No two colors are chosen the same positive number of times. 2. For any two colors (c, d) that are chosen at least once, color c is chosen more times than color d iff color c appears more times in the original set than color d.
%C A000108 If the second requirement is lifted, the number of acceptable ways equals A000110(n+1). See related comments for A016098, A085082. (End)
%C A000108 Deutsch and Sagan prove the Catalan number C_n is odd if and only if n = 2^a - 1 for some nonnegative integer a. Lin proves for every odd Catalan number C_n, we have C_n == 1 (mod 4). - _Jonathan Vos Post_, Dec 09 2010
%C A000108 a(n) is the number of functions f:{1,2,...,n}->{1,2,...,n} such that f(1)=1 and for all n >= 1 f(n+1) <= f(n)+1. For a nice bijection between this set of functions and the set of length 2n Dyck words, see page 333 of the Fxtbook (see link below). - _Geoffrey Critzer_, Dec 16 2010
%C A000108 Postnikov (2005) defines "generalized Catalan numbers" associated with buildings (e.g., Catalan numbers of Type B, see A000984). - _N. J. A. Sloane_, Dec 10 2011
%C A000108 Number of permutations in S(n) for which length equals depth. - _Bridget Tenner_, Feb 22 2012
%C A000108 a(n) is also the number of standard Young tableau of shape (n,n). - _Thotsaporn Thanatipanonda_, Feb 25 2012
%C A000108 a(n) is the number of binary sequences of length 2n+1 in which the number of ones first exceed the number of zeros at entry 2n+1. See the example below in the example section. - _Dennis P. Walsh_, Apr 11 2012
%C A000108 Number of binary necklaces of length 2*n+1 containing n 1's (or, by symmetry, 0's). All these are Lyndon words and their representatives (as cyclic maxima) are the binary Dyck words. - _Joerg Arndt_, Nov 12 2012
%C A000108 Number of sequences consisting of n 'x' letters and n 'y' letters such that (counting from the left) the 'x' count >= 'y' count. For example, for n=3 we have xxxyyy, xxyxyy, xxyyxy, xyxxyy and xyxyxy. - _Jon Perry_, Nov 16 2012
%C A000108 a(n) is the number of Motzkin paths of length n-1 in which the (1,0)-steps come in 2 colors. Example: a(4)=14 because, denoting U=(1,1), H=(1,0), and D=(1,-1), we have 8 paths of shape HHH, 2 paths of shape UHD, 2 paths of shape UDH, and 2 paths of shape HUD. - _José Luis Ramírez Ramírez_, Jan 16 2013
%C A000108 If p is an odd prime, then (-1)^((p-1)/2)*a((p-1)/2) mod p = 2. - _Gary Detlefs_, Feb 20 2013
%C A000108 Conjecture: For any positive integer n, the polynomial Sum_{k=0..n} a(k)*x^k is irreducible over the field of rational numbers. - _Zhi-Wei Sun_, Mar 23 2013
%C A000108 a(n) is the size of the Jones monoid on 2n points (cf. A225798). - _James Mitchell_, Jul 28 2013
%C A000108 For 0 < p < 1, define f(p) = Sum_{n>=0} a(n)*(p*(1-p))^n, then f(p) = min{1/p, 1/(1-p)}, so f(p) reaches its maximum value 2 at p = 0.5, and p*f(p) is constant 1 for 0.5 <= p < 1. - _Bob Selcoe_, Nov 16 2013 [Corrected by _Jianing Song_, May 21 2021]
%C A000108 No a(n) has the form x^m with m > 1 and x > 1. - _Zhi-Wei Sun_, Dec 02 2013
%C A000108 From _Alexander Adamchuk_, Dec 27 2013: (Start)
%C A000108 Prime p divides a((p+1)/2) for p > 3. See A120303(n) = Largest prime factor of Catalan number.
%C A000108 Reciprocal Catalan Constant C = 1 + 4*sqrt(3)*Pi/27 = 1.80613.. = A121839.
%C A000108 Log(Phi) = (125*C - 55) / (24*sqrt(5)), where C = Sum_{k>=1} (-1)^(k+1)*1/a(k). See A002390 = Decimal expansion of natural logarithm of golden ratio.
%C A000108 3-d analog of the Catalan numbers: (3n)!/(n!(n+1)!(n+2)!) = A161581(n) = A006480(n) / ((n+1)^2*(n+2)), where A006480(n) = (3n)!/(n!)^3 De Bruijn's S(3,n). (End)
%C A000108 For a relation to the inviscid Burgers's, or Hopf, equation, see A001764. - _Tom Copeland_, Feb 15 2014
%C A000108 From _Fung Lam_, May 01 2014: (Start)
%C A000108 One class of generalized Catalan numbers can be defined by g.f. A(x) = (1-sqrt(1-q*4*x*(1-(q-1)*x)))/(2*q*x) with nonzero parameter q.  Recurrence: (n+3)*a(n+2) -2*q*(2*n+3)*a(n+1) +4*q*(q-1)*n*a(n) = 0 with a(0)=1, a(1)=1.
%C A000108 Asymptotic approximation for q >= 1: a(n) ~ (2*q+2*sqrt(q))^n*sqrt(2*q*(1+sqrt(q))) /sqrt(4*q^2*Pi*n^3).
%C A000108 For q <= -1, the g.f. defines signed sequences with asymptotic approximation: a(n) ~ Re(sqrt(2*q*(1+sqrt(q)))*(2*q+2*sqrt(q))^n) / sqrt(q^2*Pi*n^3), where Re denotes the real part. Due to Stokes' phenomena, accuracy of the asymptotic approximation deteriorates at/near certain values of n.
%C A000108 Special cases are A000108 (q=1), A068764 to A068772 (q=2 to 10), A240880 (q=-3).
%C A000108 (End)
%C A000108 Number of sequences [s(0), s(1), ..., s(n)] with s(n)=0, Sum_{j=0..n} s(j) = n, and Sum_{j=0..k} s(j)-1 >= 0 for k < n-1 (and necessarily Sum_{j=0..n-1} s(j)-1 = 0).  These are the branching sequences of the (ordered) trees with n non-root nodes, see example. - _Joerg Arndt_, Jun 30 2014
%C A000108 Number of stack-sortable permutations of [n], these are the 231-avoiding permutations; see the Bousquet-Mélou reference. - _Joerg Arndt_, Jul 01 2014
%C A000108 a(n) is the number of increasing strict binary trees with 2n-1 nodes that avoid 132. For more information about increasing strict binary trees with an associated permutation, see A245894. - _Manda Riehl_, Aug 07 2014
%C A000108 In a one-dimensional medium with elastic scattering (zig-zag walk), first recurrence after 2n+1 scattering events has the probability C(n)/2^(2n+1). - _Joachim Wuttke_, Sep 11 2014
%C A000108 The o.g.f. C(x) = (1 - sqrt(1-4x))/2, for the Catalan numbers, with comp. inverse Cinv(x) = x*(1-x) and the functions P(x) = x / (1 + t*x) and its inverse Pinv(x,t) = -P(-x,t) = x / (1 - t*x) form a group under composition that generates or interpolates among many classic arrays, such as the Motzkin (Riordan, A005043), Fibonacci (A000045), and Fine (A000957) numbers and polynomials (A030528), and enumerating arrays for Motzkin, Dyck, and Łukasiewicz lattice paths and different types of trees and non-crossing partitions (A091867, connected to sums of the refined Narayana numbers A134264). - _Tom Copeland_, Nov 04 2014
%C A000108 Conjecture: All the rational numbers Sum_{i=j..k} 1/a(i) with 0 < min{2,k} <= j <= k have pairwise distinct fractional parts. - _Zhi-Wei Sun_, Sep 24 2015
%C A000108 The Catalan number series A000108(n+3), offset n=0, gives Hankel transform revealing the square pyramidal numbers starting at 5, A000330(n+2), offset n=0 (empirical observation). - _Tony Foster III_, Sep 05 2016
%C A000108 Hankel transforms of the Catalan numbers with the first 2, 4, and 5 terms omitted give A001477, A006858, and A091962, respectively, without the first 2 terms in all cases. More generally, the Hankel transform of the Catalan numbers with the first k terms omitted is H_k(n) = Product_{j=1..k-1} Product_{i=1..j} (2*n+j+i)/(j+i) [see Cigler (2011), Eq. (1.14) and references therein]; together they form the array A078920/A123352/A368025. - _Andrey Zabolotskiy_, Oct 13 2016
%C A000108 Presumably this satisfies Benford's law, although the results in Hürlimann (2009) do not make this clear. See S. J. Miller, ed., 2015, p. 5. - _N. J. A. Sloane_, Feb 09 2017
%C A000108 Coefficients of the generating series associated to the Magmatic and Dendriform operadic algebras. Cf. p. 422 and 435 of the Loday et al. paper. - _Tom Copeland_, Jul 08 2018
%C A000108 Let M_n be the n X n matrix with M_n(i,j) = binomial(i+j-1,2j-2); then det(M_n) = a(n). - _Tony Foster III_, Aug 30 2018
%C A000108 Also the number of Catalan trees, or planted plane trees (Bona, 2015, p. 299, Theorem 4.6.3). - _N. J. A. Sloane_, Dec 25 2018
%C A000108 Number of coalescent histories for a caterpillar species tree and a matching caterpillar gene tree with n+1 leaves (Rosenberg 2007, Corollary 3.5). - _Noah A Rosenberg_, Jan 28 2019
%C A000108 Finding solutions of eps*x^2+x-1 = 0 for eps small, that is, writing x = Sum_{n>=0} x_{n}*eps^n and expanding, one finds x = 1 - eps + 2*eps^2 - 5*eps^3 + 14*eps^3 - 42*eps^4 + ... with x_{n} = (-1)^n*C(n). Further, letting x = 1/y and expanding y about 0 to find large roots, that is, y = Sum_{n>=1} y_{n}*eps^n, one finds y = 0 - eps + eps^2 - 2*eps^3 + 5*eps^3 - ... with y_{n} = (-1)^n*C(n-1).  - _Derek Orr_, Mar 15 2019
%C A000108 Permutations of length n that produce a bipartite permutation graph of order n [see Knuth (1973), Busch (2006), Golumbic and Trenk (2004)]. - _Elise Anderson_, _R. M. Argus_, _Caitlin Owens_, _Tessa Stevens_, Jun 27 2019
%C A000108 For n > 0, a random selection of n + 1 objects (the minimum number ensuring one pair by the pigeonhole principle) from n distinct pairs of indistinguishable objects contains only one pair with probability 2^(n-1)/a(n) = b(n-1)/A098597(n), where b is the 0-offset sequence with the terms of A120777 repeated (1,1,4,4,8,8,64,64,128,128,...). E.g., randomly selecting 6 socks from 5 pairs that are black, blue, brown, green, and white, results in only one pair of the same color with probability 2^(5-1)/a(5) = 16/42 = 8/21 = b(4)/A098597(5). - _Rick L. Shepherd_, Sep 02 2019
%C A000108 See Haran & Tabachnikov link for a video discussing Conway-Coxeter friezes. The Conway-Coxeter friezes with n nontrivial rows are generated by the counts of triangles at each vertex in the triangulations of regular n-gons, of which there are a(n). - _Charles R Greathouse IV_, Sep 28 2019
%C A000108 For connections to knot theory and scattering amplitudes from Feynman diagrams, see Broadhurst and Kreimer, and Todorov. Eqn. 6.12 on p. 130 of Bessis et al. becomes, after scaling, -12g * r_0(-y/(12g)) = (1-sqrt(1-4y))/2, the o.g.f. (expressed as a Taylor series in Eqn. 7.22 in 12gx) given for the Catalan numbers in Copeland's (Sep 30 2011) formula below. (See also Mizera p. 34, Balduf pp. 79-80, Keitel and Bartosch.) - _Tom Copeland_, Nov 17 2019
%C A000108 Number of permutations in S_n whose principal order ideals in the weak order are modular lattices. - _Bridget Tenner_, Jan 16 2020
%C A000108 Number of permutations in S_n whose principal order ideals in the weak order are distributive lattices. - _Bridget Tenner_, Jan 16 2020
%C A000108 Legendre gives the following formula for computing the square root modulo 2^m:
%C A000108   sqrt(1 + 8*a) mod 2^m = (1 + 4*a*Sum_{i=0..m-4} C(i)*(-2*a)^i) mod 2^m
%C A000108   as cited by L. D. Dickson, History of the Theory of Numbers, Vol. 1, 207-208. - _Peter Schorn_, Feb 11 2020
%C A000108 a(n) is the number of length n permutations sorted to the identity by a consecutive-132-avoiding stack followed by a classical-21-avoiding stack. - _Kai Zheng_, Aug 28 2020
%C A000108 Number of non-crossing partitions of a 2*n-set with n blocks of size 2. Also number of non-crossing partitions of a 2*n-set with n+1 blocks of size at most 3, and without cyclical adjacencies. The two partitions can be mapped by rotated Kreweras bijection. - _Yuchun Ji_, Jan 18 2021
%C A000108 Named by Riordan (1968, and earlier in Mathematical Reviews, 1948 and 1964) after the French and Belgian mathematician Eugène Charles Catalan (1814-1894) (see Pak, 2014). - _Amiram Eldar_, Apr 15 2021
%C A000108 For n >= 1, a(n-1) is the number of interpretations of x^n is an algebra where power-associativity is not assumed. For example, for n = 4 there are a(3) = 5 interpretations: x(x(xx)), x((xx)x), (xx)(xx), (x(xx))x, ((xx)x)x. See the link "Non-associate powers and a functional equation" from I. M. H. Etherington and the page "Nonassociative Product" from Eric Weisstein's World of Mathematics for detailed information. See also A001190 for the case where multiplication is commutative. - _Jianing Song_, Apr 29 2022
%C A000108 Number of states in the transition diagram associated with the Laplacian system over the complete graph K_N, corresponding to ordered initial conditions x_1 < x_2 < ... < x_N. - _Andrea Arlette España_, Nov 06 2022
%C A000108 a(n) is the number of 132-avoiding stabilized-interval-free permutations of size n+1. - _Juan B. Gil_, Jun 22 2023
%C A000108 Number of rooted polyominoes composed of n triangular cells of the hyperbolic regular tiling with Schläfli symbol {3,oo}. A rooted polyomino has one external edge identified, and chiral pairs are counted as two. A stereographic projection of the {3,oo} tiling on the Poincaré disk can be obtained via the Christensson link. - _Robert A. Russell_, Jan 27 2024
%C A000108 a(n) is the number of extremely lucky Stirling permutations of order n; i.e., the number of Stirling permutations of order n that have exactly n lucky cars. (see Colmenarejo et al. reference) - _Bridget Tenner_, Apr 16 2024
%D A000108 The large number of references and links demonstrates the ubiquity of the Catalan numbers.
%D A000108 R. Alter, Some remarks and results on Catalan numbers, pp. 109-132 in Proceedings of the Louisiana Conference on Combinatorics, Graph Theory and Computer Science. Vol. 2, edited R. C. Mullin et al., 1971.
%D A000108 Miklos Bona, editor, Handbook of Enumerative Combinatorics, CRC Press, 2015, many references.
%D A000108 L. Comtet, Advanced Combinatorics, Reidel, 1974, p. 53.
%D A000108 J. H. Conway and R. K. Guy, The Book of Numbers, New York: Springer-Verlag, 1995, ch. 4, pp. 96-106.
%D A000108 S. J. Cyvin and I. Gutman, Kekulé structures in benzenoid hydrocarbons, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988 (see pp. 183, 196, etc.).
%D A000108 Michael Dairyko, Samantha Tyner, Lara Pudwell, and Casey Wynn, Non-contiguous pattern avoidance in binary trees. Electron. J. Combin. 19 (2012), no. 3, Paper 22, 21 pp. MR2967227.
%D A000108 E. Deutsch, Dyck path enumeration, Discrete Math., 204, 167-202, 1999.
%D A000108 E. Deutsch and L. Shapiro, Seventeen Catalan identities, Bulletin of the Institute of Combinatorics and its Applications, 31, 31-38, 2001.
%D A000108 L. E. Dickson, History of the Theory of Numbers. Carnegie Institute Public. 256, Washington, DC, Vol. 1, 1919; Vol. 2, 1920; Vol. 3, 1923, see vol. 1, 207-208.
%D A000108 Tomislav Doslic and Darko Veljan, Logarithmic behavior of some combinatorial sequences. Discrete Math. 308 (2008), no. 11, 2182-2212. MR2404544 (2009j:05019)
%D A000108 S. Dulucq and J.-G. Penaud, Cordes, arbres et permutations. Discrete Math. 117 (1993), no. 1-3, 89-105.
%D A000108 A. Errera, Analysis situs - Un problème d'énumération, Mémoires Acad. Bruxelles, Classe des sciences, Série 2, Vol. XI, Fasc. 6, No. 1421 (1931), 26 pp.
%D A000108 Ehrenfeucht, Andrzej; Haemer, Jeffrey; Haussler, David. Quasimonotonic sequences: theory, algorithms and applications. SIAM J. Algebraic Discrete Methods 8 (1987), no. 3, 410-429. MR0897739 (88h:06026)
%D A000108 I. M. H. Etherington, Non-associate powers and a functional equation. The Mathematical Gazette, 21 (1937): 36-39; addendum 21 (1937), 153.
%D A000108 I. M. H. Etherington, On non-associative combinations, Proc. Royal Soc. Edinburgh, 59 (Part 2, 1938-39), 153-162.
%D A000108 I. M. H. Etherington, Some problems of non-associative combinations (I), Edinburgh Math. Notes, 32 (1940), pp. i-vi. Part II is by A. Erdelyi and I. M. H. Etherington, and is on pages vii-xiv of the same issue.
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%H A000108 P. Peart and W.-J. Woan, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL3/PEART/peart1.html">Generating Functions via Hankel and Stieltjes Matrices</a>, J. Integer Seqs., Vol. 3 (2000), #00.2.1.
%H A000108 P. Peart and W.-J. Woan, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL4/PEART/pwatjis2.html">Dyck Paths With No Peaks at Height k</a>, J. Integer Sequences, 4 (2001), #01.1.3.
%H A000108 Robin Pemantle and Mark C. Wilson, <a href="http://dx.doi.org/10.1137/050643866">Twenty Combinatorial Examples of Asymptotics Derived from Multivariate Generating Functions</a>, SIAM Rev., 50 (2) (2008), 199-272.
%H A000108 K. A. Penson and J.-M. Sixdeniers, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL4/SIXDENIERS/Catalan.html">Integral Representations of Catalan and Related Numbers</a>, J. Integer Sequences, 4 (2001), #01.2.5.
%H A000108 Karol A. Penson and Karol Zyczkowski, <a href="http://dx.doi.org/10.1103/PhysRevE.83.061118">Product of Ginibre matrices : Fuss-Catalan and Raney distribution</a>, <a href="http://arxiv.org/abs/1103.3453/">arXiv version</a>; Phys. Rev E. vol. 83, 061118 (2011).
%H A000108 Permutation Pattern Avoidance Library (PermPAL), <a href="https://permpal.com/perms/name/021/">021</a>
%H A000108 T. K. Petersen and Bridget Eileen Tenner, <a href="http://arxiv.org/abs/1202.4765">The depth of a permutation</a>, arXiv:1202.4765 [math.CO], 2012-2014.
%H A000108 Ville H. Pettersson, <a href="http://www.combinatorics.org/ojs/index.php/eljc/article/view/v21i4p7">Enumerating Hamiltonian Cycles</a>, The Electronic Journal of Combinatorics, Volume 21, Issue 4, 2014.
%H A000108 Vincent Pilaud, <a href="http://arxiv.org/abs/1505.07665">Brick polytopes, lattice quotients, and Hopf algebras</a>, arXiv preprint arXiv:1505.07665 [math.CO], 2015.
%H A000108 Vincent Pilaud, <a href="https://arxiv.org/abs/2205.06686">Pebble trees</a>, arXiv:2205.06686 [math.CO], 2022.
%H A000108 Maxim V. Polyakov, Kirill M. Semenov-Tian-Shansky, Alexander O. Smirnov and Alexey A. Vladimirov, <a href="https://arxiv.org/abs/1811.08449">Quasi-Renormalizable Quantum Field Theories</a>, arXiv:1811.08449 [hep-th], 2018.
%H A000108 Alexander Postnikov, <a href="http://arxiv.org/abs/math/0507163">Permutohedra, associahedra, and beyond</a>, 2005, arXiv:math/0507163  [math.CO], 2005.
%H A000108 J.-B. Priez and A. Virmaux, <a href="http://arxiv.org/abs/1411.4161">Non-commutative Frobenius characteristic of generalized parking functions: Application to enumeration</a>, arXiv preprint arXiv:1411.4161 [math.CO], 2014-2015.
%H A000108 L. Pudwell and A. Baxter, <a href="http://faculty.valpo.edu/lpudwell/slides/pp2014_pudwell.pdf">Ascent sequences avoiding pairs of patterns</a>, 2014.
%H A000108 Alon Regev, <a href="http://arxiv.org/abs/1208.3915">Enumerating Triangulations by Parallel Diagonals</a>, Journal of Integer Sequences, Vol. 15 (2012), #12.8.5; arXiv preprint arXiv:1208.3915, 2012.
%H A000108 Alon Regev, Amitai Regev, and Doron Zeilberger, <a href="http://arxiv.org/abs/1507.03499">Identities in character tables of S_n</a>, arXiv preprint arXiv:1507.03499 [math.CO], 2015.
%H A000108 Amitai Regev, Nathaniel Shar, and Doron Zeilberger, <a href="http://sites.math.rutgers.edu/~zeilberg/mamarim/mamarimhtml/touchard.html">A Very Short (Bijective!) Proof of Touchard's Catalan Identity</a>, 2015.
%H A000108 Amitai Regev, Nathaniel Shar, and Doron Zeilberger, <a href="/A000108/a000108_21.pdf">A Very Short (Bijective!) Proof of Touchard's Catalan Identity</a>, [Local copy, pdf file only, no active links]
%H A000108 J.-L. Rémy, <a href="https://doi.org/10.1051/ita/1985190201791">Un procédé itératif de dénombrement d'arbres binaires et son application à leur génération aléatoire</a>, RAIRO Inform. Theor. 19 (1985), 179-195.
%H A000108 C. M. Ringel, <a href="http://arxiv.org/abs/1502.06553">The Catalan combinatorics of the hereditary artin algebras</a>, arXiv preprint arXiv:1502.06553 [math.RT], 2015.
%H A000108 J. Riordan, <a href="http://www.jstor.org/stable/2005477">The distribution of crossings of chords joining pairs of 2n points on a circle</a>, Math. Comp., 29 (1975), 215-222.
%H A000108 J. Riordan, <a href="/A003480/a003480.pdf">The distribution of crossings of chords joining pairs of 2n points on a circle</a>, Math. Comp., 29 (1975), 215-222. [Annotated scanned copy]
%H A000108 N. A. Rosenberg, <a href="https://doi.org/10.1089/cmb.2006.0109">Counting coalescent histories</a>, J. Comput Biol., 14 (2007), 360-377.
%H A000108 E. Rowland and R. Yassawi, <a href="http://arxiv.org/abs/1310.8635">Automatic congruences for diagonals of rational functions</a>, arXiv preprint arXiv:1310.8635 [math.NT], 2013-2014.
%H A000108 E. Rowland and D. Zeilberger, <a href="http://arxiv.org/abs/1311.4776">A Case Study in Meta-AUTOMATION: AUTOMATIC Generation of Congruence AUTOMATA For Combinatorial Sequences</a>, arXiv preprint arXiv:1311.4776 [math.CO], 2013.
%H A000108 Albert Sade, <a href="/A000108/a000108_17.pdf">Sur les Chevauchements des Permutations</a>, published by the author, Marseille, 1949. [Annotated scanned copy]
%H A000108 A. Sapounakis, I. Tasoulas and P. Tsikouras, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL9/Tsikouras/tsikouras67.html">On the Dominance Partial Ordering of Dyck Paths</a>, Journal of Integer Sequences, Vol. 9 (2006), Article 06.2.5.
%H A000108 A. Sapounakis and P. Tsikouras, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL7/Tsikouras/tsikouras43.html">On k-colored Motzkin words</a>, Journal of Integer Sequences, Vol. 7 (2004), Article 04.2.5.
%H A000108 E. Schröder, <a href="/A000108/a000108_9.pdf">Vier combinatorische Probleme</a>, Z. f. Math. Phys., 15 (1870), 361-376. [Annotated scanned copy]
%H A000108 A. Schuetz and G. Whieldon, <a href="http://arxiv.org/abs/1401.7194">Polygonal Dissections and Reversions of Series</a>, arXiv preprint arXiv:1401.7194 [math.CO], 2014.
%H A000108 J. A. von Segner, <a href="https://archive.org/details/novicommentariia07impe/page/203">Enumeratio modorum, quibus figurae planae rectilineae per diagonales dividuntur in triangula</a>, Novi Comm. Acad. Scient. Imper. Petropolitanae, 7 (1758/1759), 203-209.
%H A000108 Sarah Shader, <a href="http://math.mit.edu/news/summer/RSIPapers/2013Shader.pdf">Weighted Catalan Numbers and Their Divisibility Properties</a>, Research Science Institute, MIT, 2014.
%H A000108 L. W. Shapiro, <a href="http://dx.doi.org/10.1016/0012-365X(76)90009-1">A Catalan triangle</a>, Discrete Math., 14, 83-90, 1976.
%H A000108 L. W. Shapiro, <a href="/A003517/a003517.pdf">A Catalan triangle</a>, Discrete Math. 14 (1976), no. 1, 83-90. [Annotated scanned copy]
%H A000108 D. M. Silberger, <a href="/A000108/a000108_12.pdf">Occurrences of the integer (2n-2)!/n!(n-1)!</a>, Roczniki Polskiego Towarzystwa Math. 13 (1969): 91-96. [Annotated scanned copy]
%H A000108 N. J. A. Sloane, <a href="/A000108/a000108.html">Illustration of initial terms</a>
%H A000108 N. J. A. Sloane, <a href="/A000108/a000108_16.pdf">Note on Sylvester's "On reducible cyclodes" paper</a> [Scanned copy]
%H A000108 N. J. A. Sloane, <a href="https://arxiv.org/abs/2301.03149">"A Handbook of Integer Sequences" Fifty Years Later</a>, arXiv:2301.03149 [math.NT], 2023, p. 7.
%H A000108 Solomon, A. <a href="https://gdz.sub.uni-goettingen.de/id/PPN362162808_0053">Catalan monoids, monoids of local endomorphisms and their presentations</a>, Semigroup Forum 53 (1996), 351-368.
%H A000108 N. Solomon and S. Solomon, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL11/Solomon/solomon8rev.html">A natural extension of Catalan Numbers</a>, JIS 11 (2008) 08.3.5
%H A000108 Frank Sottile, <a href="http://www.math.tamu.edu/~sottile/research/pages/ERAG/S4/1.html">The Schubert Calculus of Lines</a> (a section of Enumerative Real Algebraic Geometry)
%H A000108 Michael Z. Spivey and Laura L. Steil, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL9/Spivey/spivey7.html">The k-Binomial Transforms and the Hankel Transform</a>, Journal of Integer Sequences, Vol. 9 (2006), Article 06.1.1.
%H A000108 R. P. Stanley, <a href="http://www-math.mit.edu/~rstan/papers.html">Hipparchus, Plutarch, Schröder and Hough</a>, Am. Math. Monthly, Vol. 104, No. 4, p. 344, 1997.
%H A000108 R. P. Stanley, <a href="http://www-math.mit.edu/~rstan/ec/catalan.pdf">Exercises on Catalan and Related Numbers</a>
%H A000108 R. P. Stanley, <a href="http://www-math.mit.edu/~rstan/ec#catadd">Catalan Addendum</a>
%H A000108 R. P. Stanley, <a href="/A000108/a000108.pdf">Interpretations of Catalan Numbers (Notes)</a> [Annotated scanned copy]
%H A000108 P. J. Stockmeyer, <a href="/A006078/a006078.pdf">The charm bracelet problem and its applications</a>, pp. 339-349 of Graphs and Combinatorics (Washington, Jun 1973), Ed. by R. A. Bari and F. Harary. Lect. Notes Math., Vol. 406. Springer-Verlag, 1974. [Scanned annotated and corrected copy]
%H A000108 T. Stojadinovic, <a href="https://doi.org/10.13140/RG.2.1.2996.9129">The Catalan numbers</a>, Preprint 2015.
%H A000108 C. Stump, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL17/Stump/stump4.html">On a New Collection of Words in the Catalan Family</a>, J. Int. Seq. 17 (2014) # 14.7.1
%H A000108 Zhi-Wei Sun and Roberto Tauraso, <a href="http://arxiv.org/abs/0709.1665">On some new congruences for binomial coefficients</a>, arXiv:0709.1665 [math.NT], 2007-2011.
%H A000108 V. S. Sunder, <a href="http://www.imsc.res.in/~sunder/catalan.pdf">Catalan numbers</a>
%H A000108 P. Tarau, <a href="https://pdfs.semanticscholar.org/eefb/e30e99067c8077e133749d83734b5daf188b.pdf">Computing with Catalan Families</a>, 2013, <a href="https://doi.org/10.1007/978-3-319-28228-2_8">doi:10.1007/978-3-319-28228-2_8</a>.
%H A000108 P. Tarau, <a href="http://arxiv.org/abs/1406.1796">A Generic Numbering System based on Catalan Families of Combinatorial Objects</a>, arXiv preprint arXiv:1406.1796 [cs.MS], 2014.
%H A000108 P. Tarau, <a href="http://arxiv.org/abs/1507.06944">A Logic Programming Playground for Lambda Terms, Combinators, Types and Tree-based Arithmetic Computations</a>, arXiv preprint arXiv:1507.06944 [cs.LO], 2015.
%H A000108 I. Tasoulas, K. Manes, A. Sapounakis and P. Tsikouras, <a href="https://arxiv.org/abs/1911.10883">Chains with Small Intervals in the Lattice of Binary Paths</a>, arXiv:1911.10883 [math.CO], 2019.
%H A000108 D. Taylor, <a href="http://www.maths.usyd.edu.au/u/don/code/Catalan/Catalan.html">Catalan Structures(up to C(7))</a>.
%H A000108 B. E. Tenner, <a href="https://arxiv.org/abs/2001.05011">Interval structures in the Bruhat and weak orders</a>, arXiv:2001.05011 [math.CO], 2020.
%H A000108 Thotsaporn "Aek" Thanatipanonda and Doron Zeilberger, <a href="https://arxiv.org/abs/1909.11546">A Multi-Computational Exploration of Some Games of Pure Chance</a>, arXiv:1909.11546 [math.CO], 2019.
%H A000108 I. Todorov, <a href="https://arxiv.org/abs/1311.7258">Studying Quantum Field Theory</a>, arXiv:1311.7258 [math-ph], 2013.
%H A000108 Michael Torpey, <a href="https://doi.org/10.17630/10023-17350">Semigroup congruences: computational techniques and theoretical applications</a>, Ph.D. Thesis, University of St. Andrews (Scotland, 2019).
%H A000108 J.-D. Urbina, J. Kuipers, Q. Hummel and K. Richter, <a href="http://arxiv.org/abs/1409.1558">Multiparticle correlations in complex scattering and the mesoscopic Boson Sampling problem</a>, arXiv preprint arXiv:1409.1558 [quant-ph], 2014.
%H A000108 A. Vieru, <a href="http://arxiv.org/abs/1107.2938">Agoh's conjecture: its proof, its generalizations, its analogues</a>, arXiv:1107.2938 [math.NT], 2011.
%H A000108 Gérard Villemin, <a href="http://villemin.gerard.free.fr/aNombre/TYPDENOM/Catalan/Catalan.htm">Nombres De Catalan</a> (French)
%H A000108 D. W. Walkup, <a href="http://dx.doi.org/10.1112/S0025579300005659">The number of plane trees</a>, Mathematika, vol. 19, No. 2 (1972), 200-204.
%H A000108 Wenxi Wang, Muhammad Usman, Alyas Almaawi, Kaiyuan Wang, Kuldeep S. Meel and Sarfraz Khurshid, <a href="https://www.comp.nus.edu.sg/~meel/Papers/tacas20.pdf">A Study of Symmetry Breaking Predicates and Model Counting</a>, National University of Singapore (2020).
%H A000108 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/BinaryBracketing.html">Binary Bracketing</a>.
%H A000108 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/BinaryTree.html">Binary Tree</a>.
%H A000108 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/CatalanNumber.html">Catalan Number</a>.
%H A000108 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/DyckPath.html">Dyck Path</a>.
%H A000108 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/NonassociativeProduct.html">Nonassociative Product</a>.
%H A000108 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/StaircaseWalk.html">Staircase Walk</a>.
%H A000108 Wikipedia, <a href="https://en.wikipedia.org/wiki/Catalan_number">Catalan number</a>.
%H A000108 Herbert S. Wilf, <a href="https://www2.math.upenn.edu/~wilf/DownldGF.html">Generatingfunctionology</a>, Academic Press, NY, 1990. See p. 50.
%H A000108 J. Winter, M. M. Bonsangue and J. J. M. M. Rutten, <a href="https://ir.cwi.nl/pub/21313">Context-free coalgebras</a>, 2013.
%H A000108 Roman Witula, Damian Slota and Edyta Hetmaniok, <a href="http://ami.ektf.hu/uploads/papers/finalpdf/AMI_41_from255to263.pdf">Bridges between different known integer sequences</a>, Annales Mathematicae et Informaticae, 41 (2013) pp. 255-263.
%H A000108 W.-J. Woan, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL4/WOAN/hankel2.html">Hankel Matrices and Lattice Paths</a>, J. Integer Sequences, 4 (2001), #01.1.2.
%H A000108 Wen-jin Woan, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL8/Woan/woan11.html">A Recursive Relation for Weighted Motzkin Sequences</a> Journal of Integer Sequences, Vol. 8 (2005), Article 05.1.6.
%H A000108 Wen-jin Woan, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL8/Woan2/woan35.html">Animals and 2-Motzkin Paths</a>, Journal of Integer Sequences, Vol. 8 (2005), Article 05.5.6.
%H A000108 Wen-jin Woan, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL9/Woan/woan206.html">A Relation Between Restricted and Unrestricted Weighted Motzkin Paths</a>, Journal of Integer Sequences, Vol. 9 (2006), Article 06.1.7.
%H A000108 Chunyan Yan and Zhicong Lin, <a href="https://arxiv.org/abs/1912.03674">Inversion sequences avoiding pairs of patterns</a>, arXiv:1912.03674 [math.CO], 2019.
%H A000108 F. Yano and H. Yoshida, <a href="http://dx.doi.org/10.1016/j.disc.2007.03.050">Some set partition statistics in non-crossing partitions and generating functions</a>, Discr. Math., 307 (2007), 3147-3160.
%H A000108 Yan X Zhang, <a href="http://arxiv.org/abs/1508.00318">Four Variations on Graded Posets</a>, arXiv preprint arXiv:1508.00318 [math.CO], 2015.
%H A000108 <a href="/index/Cor#core">Index entries for "core" sequences</a>
%H A000108 <a href="/index/Ne#necklaces">Index entries for sequences related to necklaces</a>
%H A000108 <a href="/index/Par#parens">Index entries for sequences related to parenthesizing</a>
%H A000108 <a href="/index/Ro#rooted">Index entries for sequences related to rooted trees</a>
%H A000108 <a href="/index/Be#Benford">Index entries for sequences related to Benford's law</a>
%F A000108 a(n) = binomial(2*n, n)/(n+1) = (2*n)!/(n!*(n+1)!) = A000984(n)/(n+1).
%F A000108 Recurrence: a(n) = 2*(2*n-1)*a(n-1)/(n+1) with a(0) = 1.
%F A000108 Recurrence: a(n) = Sum_{k=0..n-1} a(k)a(n-1-k).
%F A000108 G.f.: A(x) = (1 - sqrt(1 - 4*x)) / (2*x), and satisfies A(x) = 1 + x*A(x)^2.
%F A000108 a(n) = Product_{k=2..n} (1 + n/k).
%F A000108 a(n+1) = Sum_{i} binomial(n, 2*i)*2^(n-2*i)*a(i). - Touchard
%F A000108 It is known that a(n) is odd if and only if n=2^k-1, k=0, 1, 2, 3, ... - _Emeric Deutsch_, Aug 04 2002, corrected by _M. F. Hasler_, Nov 08 2015
%F A000108 Using the Stirling approximation in A000142 we get the asymptotic expansion a(n) ~ 4^n / (sqrt(Pi * n) * (n + 1)). - Dan Fux (dan.fux(AT)OpenGaia.com or danfux(AT)OpenGaia.com), Apr 13 2001
%F A000108 Integral representation: a(n) = (1/(2*Pi))*Integral_{x=0..4} x^n*sqrt((4-x)/x). - _Karol A. Penson_, Apr 12 2001
%F A000108 E.g.f.: exp(2*x)*(I_0(2*x)-I_1(2*x)), where I_n is Bessel function. - _Karol A. Penson_, Oct 07 2001
%F A000108 a(n) = polygorial(n, 6)/polygorial(n, 3). - Daniel Dockery (peritus(AT)gmail.com), Jun 24 2003
%F A000108 G.f. A(x) satisfies ((A(x) + A(-x)) / 2)^2 = A(4*x^2). - _Michael Somos_, Jun 27 2003
%F A000108 G.f. A(x) satisfies Sum_{k>=1} k(A(x)-1)^k = Sum_{n>=1} 4^{n-1}*x^n. - Shapiro, Woan, Getu
%F A000108 a(n+m) = Sum_{k} A039599(n, k)*A039599(m, k). - _Philippe Deléham_, Dec 22 2003
%F A000108 a(n+1) = (1/(n+1))*Sum_{k=0..n} a(n-k)*binomial(2k+1, k+1). - _Philippe Deléham_, Jan 24 2004
%F A000108 a(n) = Sum_{k>=0} A008313(n, k)^2. - _Philippe Deléham_, Feb 14 2004
%F A000108 a(m+n+1) = Sum_{k>=0} A039598(m, k)*A039598(n, k). - _Philippe Deléham_, Feb 15 2004
%F A000108 a(n) = Sum_{k=0..n} (-1)^k*2^(n-k)*binomial(n, k)*binomial(k, floor(k/2)). - _Paul Barry_, Jan 27 2005
%F A000108 Sum_{n>=0} 1/a(n) = 2 + 4*Pi/3^(5/2) = F(1,2;1/2;1/4) = A268813 = 2.806133050770763... (see L'Univers de Pi link). - _Gerald McGarvey_ and _Benoit Cloitre_, Feb 13 2005
%F A000108 a(n) = Sum_{k=0..floor(n/2)} ((n-2*k+1)*binomial(n, n-k)/(n-k+1))^2, which is equivalent to: a(n) = Sum_{k=0..n} A053121(n, k)^2, for n >= 0. - _Paul D. Hanna_, Apr 23 2005
%F A000108 a((m+n)/2) = Sum_{k>=0} A053121(m, k)*A053121(n, k) if m+n is even. - _Philippe Deléham_, May 26 2005
%F A000108 E.g.f. Sum_{n>=0} a(n) * x^(2*n) / (2*n)! = BesselI(1, 2*x) / x. - _Michael Somos_, Jun 22 2005
%F A000108 Given g.f. A(x), then B(x) = x * A(x^3) satisfies 0 = f(x, B(X)) where f(u, v) = u - v + (u*v)^2 or B(x) = x + (x * B(x))^2 which implies B(-B(x)) = -x and also (1 + B^3) / B^2 = (1 - x^3) / x^2. - _Michael Somos_, Jun 27 2005
%F A000108 a(n) = a(n-1)*(4-6/(n+1)). a(n) = 2a(n-1)*(8a(n-2)+a(n-1))/(10a(n-2)-a(n-1)). - _Franklin T. Adams-Watters_, Feb 08 2006
%F A000108 Sum_{k>=1} a(k)/4^k = 1. - _Franklin T. Adams-Watters_, Jun 28 2006
%F A000108 a(n) = A047996(2*n+1, n). - _Philippe Deléham_, Jul 25 2006
%F A000108 Binomial transform of A005043. - _Philippe Deléham_, Oct 20 2006
%F A000108 a(n) = Sum_{k=0..n} (-1)^k*A116395(n,k). - _Philippe Deléham_, Nov 07 2006
%F A000108 a(n) = (1/(s-n))*Sum_{k=0..n} (-1)^k (k+s-n)*binomial(s-n,k) * binomial(s+n-k,s) with s a nonnegative free integer [H. W. Gould].
%F A000108 a(k) = Sum_{i=1..k} |A008276(i,k)| * (k-1)^(k-i) / k!. - _André F. Labossière_, May 29 2007
%F A000108 a(n) = Sum_{k=0..n} A129818(n,k) * A007852(k+1). - _Philippe Deléham_, Jun 20 2007
%F A000108 a(n) = Sum_{k=0..n} A109466(n,k) * A127632(k). - _Philippe Deléham_, Jun 20 2007
%F A000108 Row sums of triangle A124926. - _Gary W. Adamson_, Oct 22 2007
%F A000108 Limit_{n->oo} (1 + Sum_{k=0..n} a(k)/A004171(k)) = 4/Pi. - _Reinhard Zumkeller_, Aug 26 2008
%F A000108 a(n) = Sum_{k=0..n} A120730(n,k)^2 and a(k+1) = Sum_{n>=k} A120730(n,k). - _Philippe Deléham_, Oct 18 2008
%F A000108 Given an integer t >= 1 and initial values u = [a_0, a_1, ..., a_{t-1}], we may define an infinite sequence Phi(u) by setting a_n = a_{n-1} + a_0*a_{n-1} + a_1*a_{n-2} + ... + a_{n-2}*a_1 for n >= t. For example, the present sequence is Phi([1]) (also Phi([1,1])). - _Gary W. Adamson_, Oct 27 2008
%F A000108 a(n) = Sum_{l_1=0..n+1} Sum_{l_2=0..n}...Sum_{l_i=0..n-i}...Sum_{l_n=0..1} delta(l_1,l_2,...,l_i,...,l_n) where delta(l_1,l_2,...,l_i,...,l_n) = 0 if any l_i < l_(i+1) and l_(i+1) <> 0 for i=1..n-1 and delta(l_1,l_2,...,l_i,...,l_n) = 1 otherwise. - _Thomas Wieder_, Feb 25 2009
%F A000108 a(n) = A000680(n)/A006472(n+1). - _Mark Dols_, Jul 14 2010; corrected by _M. F. Hasler_, Nov 08 2015
%F A000108 Let A(x) be the g.f., then B(x)=x*A(x) satisfies the differential equation B'(x)-2*B'(x)*B(x)-1=0. - _Vladimir Kruchinin_, Jan 18 2011
%F A000108 Complement of A092459; A010058(a(n)) = 1. - _Reinhard Zumkeller_, Mar 29 2011
%F A000108 G.f.: 1/(1-x/(1-x/(1-x/(...)))) (continued fraction). - _Joerg Arndt_, Mar 18 2011
%F A000108 With F(x) = (1-2*x-sqrt(1-4*x))/(2*x) an o.g.f. in x for the Catalan series, G(x) = x/(1+x)^2 is the compositional inverse of F (nulling the n=0 term). - _Tom Copeland_, Sep 04 2011
%F A000108 With H(x) = 1/(dG(x)/dx) = (1+x)^3 / (1-x), the n-th Catalan number is given by (1/n!)*((H(x)*d/dx)^n)x evaluated at x=0, i.e., F(x) = exp(x*H(u)*d/du)u, evaluated at u = 0. Also, dF(x)/dx = H(F(x)), and H(x) is the o.g.f. for A115291. - _Tom Copeland_, Sep 04 2011
%F A000108 From _Tom Copeland_, Sep 30 2011: (Start)
%F A000108 With F(x) = (1-sqrt(1-4*x))/2 an o.g.f. in x for the Catalan series, G(x)= x*(1-x) is the compositional inverse and this relates the Catalan numbers to the row sums of A125181.
%F A000108 With H(x) = 1/(dG(x)/dx) = 1/(1-2x), the n-th Catalan number (offset 1) is given by (1/n!)*((H(x)*d/dx)^n)x evaluated at x=0, i.e., F(x) = exp(x*H(u)*d/du)u, evaluated at u = 0. Also, dF(x)/dx = H(F(x)). (End)
%F A000108 G.f.: (1-sqrt(1-4*x))/(2*x) = G(0) where G(k) = 1 + (4*k+1)*x/(k+1-2*x*(k+1)*(4*k+3)/(2*x*(4*k+3)+(2*k+3)/G(k+1))); (continued fraction). - _Sergei N. Gladkovskii_, Nov 30 2011
%F A000108 E.g.f.: exp(2*x)*(BesselI(0,2*x) - BesselI(1,2*x)) = G(0) where G(k) = 1 + (4*k+1)*x/((k+1)*(2*k+1)-x*(k+1)*(2*k+1)*(4*k+3)/(x*(4*k+3)+(k+1)*(2*k+3)/G(k+1))); (continued fraction). - _Sergei N. Gladkovskii_, Nov 30 2011
%F A000108 E.g.f.: Hypergeometric([1/2],[2],4*x) which coincides with the e.g.f. given just above, and also by _Karol A. Penson_ further above. - _Wolfdieter Lang_, Jan 13 2012
%F A000108 A076050(a(n)) = n + 1 for n > 0. - _Reinhard Zumkeller_, Feb 17 2012
%F A000108 a(n) = A208355(2*n-1) = A208355(2*n) for n > 0. - _Reinhard Zumkeller_, Mar 04 2012
%F A000108 a(n+1) = A214292(2*n+1,n) = A214292(2*n+2,n). - _Reinhard Zumkeller_, Jul 12 2012
%F A000108 G.f.: 1 + 2*x/(U(0)-2*x) where U(k) = k*(4*x+1) + 2*x + 2 - x*(2*k+3)*(2*k+4)/U(k+1); (continued fraction, Euler's 1st kind, 1-step). - _Sergei N. Gladkovskii_, Sep 20 2012
%F A000108 G.f.: hypergeom([1/2,1],[2],4*x). - _Joerg Arndt_, Apr 06 2013
%F A000108 Special values of Jacobi polynomials, in Maple notation: a(n) = 4^n*JacobiP(n,1,-1/2-n,-1)/(n+1). - _Karol A. Penson_, Jul 28 2013
%F A000108 For n > 0: a(n) = sum of row n in triangle A001263. - _Reinhard Zumkeller_, Oct 10 2013
%F A000108 a(n) = binomial(2n,n-1)/n and a(n) mod n = binomial(2n,n) mod n = A059288(n). - _Jonathan Sondow_, Dec 14 2013
%F A000108 a(n-1) = Sum_{t1+2*t2+...+n*tn=n} (-1)^(1+t1+t2+...+tn)*multinomial(t1+t2 +...+tn,t1,t2,...,tn)*a(1)^t1*a(2)^t2*...*a(n)^tn. - _Mircea Merca_, Feb 27 2014
%F A000108 a(n) = Sum_{k=1..n} binomial(n+k-1,n)/n if n > 0. _Alexander Adamchuk_, Mar 25 2014
%F A000108 a(n) = -2^(2*n+1) * binomial(n-1/2, -3/2). - _Peter Luschny_, May 06 2014
%F A000108 a(n) = (4*A000984(n) - A000984(n+1))/2. - _Stanislav Sykora_, Aug 09 2014
%F A000108 a(n) = A246458(n) * A246466(n). - _Tom Edgar_, Sep 02 2014
%F A000108 a(n) = (2*n)!*[x^(2*n)]hypergeom([],[2],x^2). - _Peter Luschny_, Jan 31 2015
%F A000108 a(n) = 4^(n-1)*hypergeom([3/2, 1-n], [3], 1). - _Peter Luschny_, Feb 03 2015
%F A000108 a(2n) = 2*A000150(2n); a(2n+1) = 2*A000150(2n+1) + a(n). - _John Bodeen_, Jun 24 2015
%F A000108 a(n) = Sum_{t=1..n+1} n^(t-1)*abs(Stirling1(n+1, t)) / Sum_{t=1..n+1} abs(Stirling1(n+1, t)), for n > 0, see (10) in Cereceda link. - _Michel Marcus_, Oct 06 2015
%F A000108 a(n) ~ 4^(n-2)*(128 + 160/N^2 + 84/N^4 + 715/N^6 - 10180/N^8)/(N^(3/2)*Pi^(1/2)) where N = 4*n+3. - _Peter Luschny_, Oct 14 2015
%F A000108 a(n) = Sum_{k=1..floor((n+1)/2)} (-1)^(k-1)*binomial(n+1-k,k)*a(n-k) if n > 0; and a(0) = 1. - _David Pasino_, Jun 29 2016
%F A000108 Sum_{n>=0} (-1)^n/a(n) = 14/25 - 24*arccsch(2)/(25*sqrt(5)) = 14/25 - 24*A002390/(25*sqrt(5)) = 0.353403708337278061333... - _Ilya Gutkovskiy_, Jun 30 2016
%F A000108 C(n) = (1/n) * Sum_{i+j+k=n-1} C(i)*C(j)*C(k)*(k+1), n >= 1. - _Yuchun Ji_, Feb 21 2016
%F A000108 C(n) = 1 + Sum_{i+j+k<n-1} C(i)*C(j)*C(k). - _Yuchun Ji_, Sep 01 2016
%F A000108 a(n) = A001700(n) - A162551(n) = binomial(2*n+1,n+1). - 2*binomial(2*n,n-1). - _Taras Goy_, Aug 09 2018
%F A000108 G.f.: A(x) = (1 - sqrt(1 - 4*x)) / (2*x) = 2F1(1/2,1;2;4*x). G.f. A(x) satisfies A = 1 + x*A^2. - _R. J. Mathar_, Nov 17 2018
%F A000108 C(n) = 1 + Sum_{i=0..n-1} A000245(i). - _Yuchun Ji_, Jan 10 2019
%F A000108 From _A.H.M. Smeets_, Apr 11 2020: (Start)
%F A000108 (1+sqrt(1+4*x))/2 = 1-Sum_{i >= 0} a(i)*(-x)^(i+1), for any complex x with |x| < 1/4; and sqrt(x+sqrt(x+sqrt(x+...))) = 1-Sum_{i >= 0} a(i)*(-x)^(i+1), for any complex x with |x| < 1/4 and x <> 0. (End)
%F A000108 a(3n+1)*a(5n+4)*a(15n+10) = a(3n+2)*a(5n+2)*a(15n+11). The first case of Catalan product equation of a triple partition of 23n+15. - _Yuchun Ji_, Sep 27 2020
%F A000108 a(n) = 4^n * (-1)^(n+1) * 3F2[{n + 1,n + 1/2,n}, {3/2,1}, -1], n >= 1. - _Sergii Voloshyn_, Oct 22 2020
%F A000108 a(n) = 2^(1 + 2 n) * (-1)^(n)/(1 + n) * 3F2[{n, 1/2 + n, 1 + n}, {1/2, 1}, -1], n >= 1. - _Sergii Voloshyn_, Nov 08 2020
%F A000108 a(n) = (1/Pi)*4^(n+1)*Integral_{x=0..Pi/2} cos(x)^(2*n)*sin(x)^2 dx. - _Greg Dresden_, May 30 2021
%F A000108 From _Peter Bala_, Aug 17 2021: (Start)
%F A000108 G.f. A(x) satisfies A(x) = 1/sqrt(1 - 4*x) * A( -x/(1 - 4*x) ) and (A(x) + A(-x))/2 = 1/sqrt(1 - 4*x) * A( -2*x/(1 - 4*x) ); these are the cases k = 0 and k = -1 of the general formula 1/sqrt(1 - 4*x) * A( (k-1)*x/(1 - 4*x) ) = Sum_{n >= 0} ((k^(n+1) - 1)/(k - 1))*Catalan(n)*x^n.
%F A000108 2 - sqrt(1 - 4*x)/A( k*x/(1 - 4*x) ) = 1 + Sum_{n >= 1} (1 + (k + 1)^n) * Catalan(n-1)*x^n. (End)
%F A000108 Sum_{n>=0} a(n)*(-1/4)^n = 2*(sqrt(2)-1) (A163960). - _Amiram Eldar_, Mar 22 2022
%F A000108 0 = a(n)*(16*a(n+1) - 10*a(n+2)) + a(n+1)*(2*a(n+1) + a(n+2)) for all n>=0. - _Michael Somos_, Dec 12 2022
%F A000108 G.f.: (offset 1) 1/G(x), with G(x) = 1 - 2*x - x^2/G(x) (Jacobi continued fraction). - _Nikolaos Pantelidis_, Feb 01 2023
%F A000108 a(n) = K^(2n+1, n, 1) for all n >= 0, where K^(n, s, x) is the Krawtchouk polynomial defined to be Sum_{k=0..s} (-1)^k * binomial(n-x, s-k) * binomial(x, k). - _Vladislav Shubin_, Aug 17 2023
%F A000108 From _Peter Bala_, Feb 03 2024: (Start)
%F A000108 The g.f. A(x) satisfies the following functional equations:
%F A000108 A(x) = 1 + x/(1 - 4*x) * A(-x/(1 - 4*x))^2,
%F A000108 A(x^2) = 1/(1 - 2*x) * A(- x/(1 - 2*x))^2 and, for arbitrary k,
%F A000108 1/(1 - k*x) * A(x/(1 - k*x))^2 = 1/(1 - (k+4)*x) * A(-x/(1 - (k+4)*x))^2. (End)
%F A000108 a(n) = A363448(n) + A363449(n). - _Julien Rouyer_, Jun 28 2024
%e A000108 From _Joerg Arndt_ and Greg Stevenson, Jul 11 2011: (Start)
%e A000108 The following products of 3 transpositions lead to a 4-cycle in S_4:
%e A000108 (1,2)*(1,3)*(1,4);
%e A000108 (1,2)*(1,4)*(3,4);
%e A000108 (1,3)*(1,4)*(2,3);
%e A000108 (1,4)*(2,3)*(2,4);
%e A000108 (1,4)*(2,4)*(3,4). (End)
%e A000108 G.f. = 1 + x + 2*x^2 + 5*x^3 + 14*x^4 + 42*x^5 + 132*x^6 + 429*x^7 + ...
%e A000108 For n=3, a(3)=5 since there are exactly 5 binary sequences of length 7 in which the number of ones first exceed the number of zeros at entry 7, namely, 0001111, 0010111, 0011011, 0100111, and 0101011. - _Dennis P. Walsh_, Apr 11 2012
%e A000108 From _Joerg Arndt_, Jun 30 2014: (Start)
%e A000108 The a(4) = 14 branching sequences of the (ordered) trees with 4 non-root nodes are (dots denote zeros):
%e A000108 01:  [ 1 1 1 1 . ]
%e A000108 02:  [ 1 1 2 . . ]
%e A000108 03:  [ 1 2 . 1 . ]
%e A000108 04:  [ 1 2 1 . . ]
%e A000108 05:  [ 1 3 . . . ]
%e A000108 06:  [ 2 . 1 1 . ]
%e A000108 07:  [ 2 . 2 . . ]
%e A000108 08:  [ 2 1 . 1 . ]
%e A000108 09:  [ 2 1 1 . . ]
%e A000108 10:  [ 2 2 . . . ]
%e A000108 11:  [ 3 . . 1 . ]
%e A000108 12:  [ 3 . 1 . . ]
%e A000108 13:  [ 3 1 . . . ]
%e A000108 14:  [ 4 . . . . ]
%e A000108 (End)
%p A000108 A000108 := n->binomial(2*n,n)/(n+1);
%p A000108 G000108 := (1 - sqrt(1 - 4*x)) / (2*x);
%p A000108 spec := [ A, {A=Prod(Z,Sequence(A))}, unlabeled ]: [ seq(combstruct[count](spec, size=n+1), n=0..42) ];
%p A000108 with(combstruct): bin := {B=Union(Z,Prod(B,B))}: seq(count([B,bin,unlabeled],size=n+1), n=0..25); # _Zerinvary Lajos_, Dec 05 2007
%p A000108 gser := series(G000108, x=0, 42): seq(coeff(gser, x, n), n=0..41); # _Zerinvary Lajos_, May 21 2008
%p A000108 seq((2*n)!*coeff(series(hypergeom([],[2],x^2),x,2*n+2),x,2*n),n=0..30); # _Peter Luschny_, Jan 31 2015
%p A000108 A000108List := proc(m) local A, P, n; A := [1, 1]; P := [1];
%p A000108 for n from 1 to m - 2 do P := ListTools:-PartialSums([op(P), A[-1]]);
%p A000108 A := [op(A), P[-1]] od; A end: A000108List(31); # _Peter Luschny_, Mar 24 2022
%t A000108 Table[(2 n)!/n!/(n + 1)!, {n, 0, 20}]
%t A000108 Table[4^n Gamma[n + 1/2]/(Sqrt[Pi] Gamma[n + 2]), {n, 0, 20}] (* _Eric W. Weisstein_, Oct 31 2024 *)
%t A000108 Table[Hypergeometric2F1[1 - n, -n, 2, 1], {n, 0, 20}] (* _Richard L. Ollerton_, Sep 13 2006 *)
%t A000108 Table[CatalanNumber @ n, {n, 0, 20}] (* _Robert G. Wilson v_, Feb 15 2011 *)
%t A000108 CatalanNumber[Range[0, 20]] (* _Eric W. Weisstein_, Oct 31 2024 *)
%t A000108 CoefficientList[InverseSeries[Series[x/Sum[x^n, {n, 0, 31}], {x, 0, 31}]]/x, x] (* _Mats Granvik_, Nov 24 2013 *)
%t A000108 CoefficientList[Series[(1 - Sqrt[1 - 4 x])/(2 x), {x, 0, 20}], x] (* _Stefano Spezia_, Aug 31 2018 *)
%o A000108 (PARI) a(n)=binomial(2*n,n)/(n+1) \\ _M. F. Hasler_, Aug 25 2012
%o A000108 (PARI) a(n) = (2*n)! / n! / (n+1)!
%o A000108 (PARI) a(n) = my(A, m); if( n<0, 0, m=1; A = 1 + x + O(x^2); while(m<=n, m*=2; A = sqrt(subst(A, x, 4*x^2)); A += (A - 1) / (2*x*A)); polcoeff(A, n));
%o A000108 (PARI) {a(n) = if( n<1, n==0, polcoeff( serreverse( x / (1 + x)^2 + x * O(x^n)), n))}; /* _Michael Somos_ */
%o A000108 (PARI) (recur(a,b)=if(b<=2,(a==2)+(a==b)+(a!=b)*(1+a/2), (1+a/b)*recur(a,b-1))); a(n)=recur(n,n); \\ _R. J. Cano_, Nov 22 2012
%o A000108 (PARI) x='x+O('x^40); Vec((1-sqrt(1-4*x))/(2*x)) \\ _Altug Alkan_, Oct 13 2015
%o A000108 (MuPAD) combinat::dyckWords::count(n) $ n = 0..38 // _Zerinvary Lajos_, Apr 14 2007
%o A000108 (Magma) C:= func< n | Binomial(2*n,n)/(n+1) >; [ C(n) : n in [0..60]];
%o A000108 (Magma) [Catalan(n): n in [0..40]]; // _Vincenzo Librandi_, Apr 02 2011
%o A000108 (Haskell)
%o A000108 import Data.List (genericIndex)
%o A000108 a000108 n = genericIndex a000108_list n
%o A000108 a000108_list = 1 : catalan [1] where
%o A000108    catalan cs = c : catalan (c:cs) where
%o A000108       c = sum $ zipWith (*) cs $ reverse cs
%o A000108 -- _Reinhard Zumkeller_, Nov 12 2011
%o A000108 a000108 = map last $ iterate (scanl1 (+) . (++ [0])) [1]
%o A000108 -- _David Spies_, Aug 23 2015
%o A000108 (Sage) [catalan_number(i) for i in range(27)] # _Zerinvary Lajos_, Jun 26 2008
%o A000108 (Sage) # Generalized algorithm of L. Seidel
%o A000108 def A000108_list(n) :
%o A000108     D = [0]*(n+1); D[1] = 1
%o A000108     b = True; h = 1; R = []
%o A000108     for i in range(2*n-1) :
%o A000108         if b :
%o A000108             for k in range(h,0,-1) : D[k] += D[k-1]
%o A000108             h += 1; R.append(D[1])
%o A000108         else :
%o A000108             for k in range(1,h, 1) : D[k] += D[k+1]
%o A000108         b = not b
%o A000108     return R
%o A000108 A000108_list(31) # _Peter Luschny_, Jun 02 2012
%o A000108 (Maxima) A000108(n):=binomial(2*n,n)/(n+1)$ makelist(A000108(n),n,0,30); /* _Martin Ettl_, Oct 24 2012 */
%o A000108 (Python)
%o A000108 from gmpy2 import divexact
%o A000108 A000108 = [1, 1]
%o A000108 for n in range(1, 10**3):
%o A000108     A000108.append(divexact(A000108[-1]*(4*n+2),(n+2))) # _Chai Wah Wu_, Aug 31 2014
%o A000108 (Python)
%o A000108 # Works in Sage also.
%o A000108 A000108 = [1]
%o A000108 for n in range(1000):
%o A000108     A000108.append(A000108[-1]*(4*n+2)//(n+2)) # _Günter Rote_, Nov 08 2023
%o A000108 (GAP) A000108:=List([0..30],n->Binomial(2*n,n)/(n+1)); # _Muniru A Asiru_, Feb 17 2018
%Y A000108 Cf. A000142, A000245, A000344, A000588, A000957, A000984, A001392, A001453, A001791, A002057, A002420, A003046, A003517, A003518, A003519, A006480, A008276, A008549, A014137, A014138, A014140, A022553 (inv. Eul. trans.), A024492, A032357, A032443, A039599, A048990, A059288, A068875, A069640, A086117, A088327 (Eul. trans.), A094216, A094638, A094639, A098597, A099731, A119822, A120304, A124926, A129763, A137697, A154559, A161581, A167892, A167893, A179277, A211611, A275431 (multisets).
%Y A000108 A row of A060854.
%Y A000108 See A001003, A001190, A001699, A000081 for other ways to count parentheses.
%Y A000108 Enumerates objects encoded by A014486.
%Y A000108 A diagonal of any of the essentially equivalent arrays A009766, A030237, A033184, A059365, A099039, A106566, A130020, A047072.
%Y A000108 Cf. A051168 (diagonal of the square array described).
%Y A000108 Cf. A033552, A176137 (partitions into Catalan numbers).
%Y A000108 Cf. A000753, A000736 (Boustrophedon transforms).
%Y A000108 Cf. A120303 (largest prime factor of Catalan number).
%Y A000108 Cf. A121839 (reciprocal Catalan constant), A268813.
%Y A000108 Cf. A038003, A119861, A119908, A120274, A120275 (odd Catalan number).
%Y A000108 Cf. A002390 (decimal expansion of natural logarithm of golden ratio).
%Y A000108 Coefficients of square root of the g.f. are A001795/A046161.
%Y A000108 For a(n) mod 6 see A259667.
%Y A000108 For a(n) in base 2 see A264663.
%Y A000108 Hankel transforms with first terms omitted: A001477, A006858, A091962, A078920, A123352, A368025.
%Y A000108 Cf. A001147, A163960.
%Y A000108 Cf. A332602 (conjectured production matrix).
%Y A000108 Polyominoes: A001683(n+2) (oriented), A000207 (unoriented), A369314 (chiral), A208355(n-1) (achiral), A001764 {4,oo}.
%K A000108 core,nonn,easy,eigen,nice,changed
%O A000108 0,3
%A A000108 _N. J. A. Sloane_