cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A000063 Symmetrical dissections of an n-gon.

Original entry on oeis.org

1, 1, 2, 4, 5, 14, 14, 39, 42, 132, 132, 424, 429, 1428, 1430, 4848, 4862, 16796, 16796, 58739, 58786, 208012, 208012, 742768, 742900, 2674426, 2674440, 9694416, 9694845, 35357670, 35357670, 129643318, 129644790, 477638700, 477638700, 1767258328, 1767263190, 6564120288
Offset: 5

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Author

Keywords

Comments

This sequence, S_n in Guy's 1958 paper, counts triangulations of a regular n-gon into n-2 triangles such that the only symmetries of the triangulation are the identity and a single reflection ("symmetry of a kite"). Triangulations related by a symmetry of the underlying n-gon do not count as distinct. - Joseph Myers, Jun 21 2012
A000108 is a subsequence, see formula. - Ralf Stephan, Aug 19 2004 (edited, Joerg Arndt, Aug 31 2014)

References

  • R. K. Guy, Dissecting a polygon into triangles, Bull. Malayan Math. Soc., Vol. 5, pp. 57-60, 1958.
  • R. K. Guy, Dissecting a polygon into triangles, Research Paper #9, Math. Dept., Univ. Calgary, 1967.
  • N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Programs

  • Mathematica
    c[n_Integer] := CatalanNumber[n]; c[] = 0; a[n] := c[Floor[n/2]-1] - c[n/4-1] - c[n/6-1]; Array[a, 40, 5] (* Jean-François Alcover, Feb 03 2016, after Joseph Myers *)
  • PARI
    C(n)=if(type(n)==type(1), binomial(2*n,n)/(n+1), 0);
    a(n)=C(floor(n/2)-1) - C(n/4-1) - C(n/6-1);
    vector(66,n, a(n+4))
    \\ Joerg Arndt, Aug 31 2014

Formula

a(2n+3) = A000108(n), n>0. - M. F. Hasler, Mar 25 2012
a(n) = Catalan(floor(n/2) - 1) - Catalan(n/4 - 1) - Catalan (n/6 - 1), where Catalan(x) = 0 for noninteger x (from Guy's 1958 paper). - Joseph Myers, Jun 21 2012

Extensions

Extended by Joseph Myers, Jun 21 2012

A000131 Number of asymmetrical dissections of n-gon.

Original entry on oeis.org

2, 5, 21, 61, 214, 669, 2240, 7330, 24695, 83257, 284928, 981079, 3410990, 11937328, 42075242, 149171958, 531866972, 1905842605, 6861162880, 24805692978, 90035940227, 327987890608, 1198853954688, 4395797189206, 16165195705544, 59609156824273, 220373268471398, 816677398144221
Offset: 7

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Author

Keywords

Comments

This sequence, U_n in Guy's 1958 paper, counts triangulations of a regular n-gon into n-2 triangles with no nonidentity symmetries. Triangulations related by a symmetry of the underlying n-gon do not count as distinct. - Joseph Myers, Jun 21 2012

References

  • R. K. Guy, Dissecting a polygon into triangles, Bull. Malayan Math. Soc., Vol. 5, pp. 57-60, 1958.
  • R. K. Guy, Dissecting a polygon into triangles, Research Paper #9, Math. Dept., Univ. Calgary, 1967.
  • N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
  • N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Crossrefs

Cf. A000063.

Programs

  • Mathematica
    catalan[n_] := Block[{c = Binomial[2 n, n]/(n + 1)}, If[IntegerQ[c], c, 0]]; f[n_] := (catalan[n - 2] - (n/2) catalan[n/2 - 1] - n*catalan[Floor[n/2] - 1] - (n/3)*catalan[n/3 - 1] + n*catalan[n/4 - 1] + n*catalan[n/6 - 1])/(2 n); Array[f, 28, 7] (* Robert G. Wilson v, Jun 23 2014 *)
  • PARI
    C(n)=if(denominator(n)==1,binomial(2*n,n)/(n+1),0)
    a(n)=(C(n-2)/n-C(n/2-1)/2-C(n\2-1)-C(n/3-1)/3+C(n/4-1)+C(n/6-1))/2 \\ Charles R Greathouse IV, Apr 05 2013

Formula

a(n) = (Catalan(n-2) - (n/2)*Catalan(n/2 - 1) - n*Catalan(floor(n/2) - 1) - (n/3)*Catalan(n/3 - 1) + n*Catalan(n/4 - 1) + n*Catalan(n/6 - 1))/(2*n), where Catalan(x) = 0 for noninteger x (derived from Guy's 1958 paper). - Joseph Myers, Jun 21 2012

Extensions

Extended by Joseph Myers, Jun 21 2012

A000912 Expansion of (sqrt(1-4x^2) - sqrt(1-4x))/(2x).

Original entry on oeis.org

1, 0, 2, 4, 14, 40, 132, 424, 1430, 4848, 16796, 58744, 208012, 742768, 2674440, 9694416, 35357670, 129643360, 477638700, 1767258328, 6564120420, 24466250224, 91482563640, 343059554864, 1289904147324, 4861946193440, 18367353072152
Offset: 0

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Author

E. K. Lloyd (E.K.Lloyd(AT)soton.ac.uk)

Keywords

Comments

Number of bond-rooted polyenoids with 2n-1 edges.
Partial sums are A129366.

References

  • S. J. Cyvin, J. Brunvoll, E. Brendsdal, B. N. Cyvin and E. K. Lloyd, Enumeration of polyene hydrocarbons: a complete mathematical solution, J. Chem. Inf. Comput. Sci., 35 (1995) 743-751

Programs

  • Maple
    c:=n->binomial(2*n,n)/(n+1):a:=proc(n) if n mod 2 = 1 then c(n+1) else c(n+1)-c(n/2) fi end: seq(a(n),n=0..28); # Emeric Deutsch, Dec 19 2004
  • Mathematica
    nn = 200; CoefficientList[Series[(Sqrt[1 - 4 x^2] - Sqrt[1 - 4 x])/(2 x), {x, 0, nn}], x] (* T. D. Noe, Jun 20 2012 *)
    Table[If[EvenQ[n],CatalanNumber[n],CatalanNumber[n]-CatalanNumber[(n-1)/ 2]],{n,0,30}] (* Harvey P. Dale, Oct 30 2013 *)

Formula

a(n) = C(n) if n is even and a(n) = C(n) -C((n-1)/2) if n is odd, where C(n) = binomial(2n, n)/(n+1) are the Catalan numbers (A000108). a(n) = 2*A000150(n) for n > 0. - Emeric Deutsch, Dec 19 2004
G.f.: c(x) - x*c(x^2), where c(x) = g.f. for A000108; a(n) = C(n) - C((n-1)/2)(1-(-1)^n)/2, C(n) = A000108(n). - Paul Barry, Apr 11 2007
D-finite with recurrence n*(n+1)*a(n) - 6*n*(n-1)*a(n-1) + 4*(2*n^2-10*n+9)*a(n-2) + 8*(n^2+n-9)*a(n-3) - 48*(n-3)*(n-4)*a(n-4) + 32*(2*n-9)*(n-5)*a(n-5) = 0. - R. J. Mathar, Nov 24 2012

Extensions

More terms from Emeric Deutsch, Dec 19 2004
Edited by N. J. A. Sloane, Jul 02 2008 at the suggestion of R. J. Mathar

A355173 The Fuss-Catalan triangle of order 1, read by rows. Related to binary trees.

Original entry on oeis.org

1, 0, 1, 0, 1, 2, 0, 1, 3, 5, 0, 1, 4, 9, 14, 0, 1, 5, 14, 28, 42, 0, 1, 6, 20, 48, 90, 132, 0, 1, 7, 27, 75, 165, 297, 429, 0, 1, 8, 35, 110, 275, 572, 1001, 1430, 0, 1, 9, 44, 154, 429, 1001, 2002, 3432, 4862, 0, 1, 10, 54, 208, 637, 1638, 3640, 7072, 11934, 16796
Offset: 0

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Author

Peter Luschny, Jun 25 2022

Keywords

Comments

The Fuss-Catalan triangle of order m is a regular, (0, 0)-based table recursively defined as follows: Set row(0) = [1] and row(1) = [0, 1]. Now assume row(n-1) already constructed and duplicate the last element of row(n-1). Next apply the cumulative sum m times to this list to get row(n). Here m = 1. (See the Python program for a reference implementation.)
This definition also includes the classical Fuss-Catalan numbers, since T(n, n) = A000108(n), or row 2 in A355262. For m = 2 see A355172 and for m = 3 A355174. More generally, for n >= 1 all Fuss-Catalan sequences (A355262(n, k), k >= 0) are the main diagonals of the Fuss-Catalan triangles of order n - 1.

Examples

			Table T(n, k) begins:
  [0] [1]
  [1] [0, 1]
  [2] [0, 1, 2]
  [3] [0, 1, 3,  5]
  [4] [0, 1, 4,  9,  14]
  [5] [0, 1, 5, 14,  28,  42]
  [6] [0, 1, 6, 20,  48,  90,  132]
  [7] [0, 1, 7, 27,  75, 165,  297, 429]
  [8] [0, 1, 8, 35, 110, 275,  572, 1001, 1430]
  [9] [0, 1, 9, 44, 154, 429, 1001, 2002, 3432, 4862]
Seen as an array reading the diagonals starting from the main diagonal:
  [0] 1, 1, 2,  5,  14,   42,  132,   429,  1430,   4862,   16796, ...  A000108
  [1] 0, 1, 3,  9,  28,   90,  297,  1001,  3432,  11934,   41990, ...  A000245
  [2] 0, 1, 4, 14,  48,  165,  572,  2002,  7072,  25194,   90440, ...  A099376
  [3] 0, 1, 5, 20,  75,  275, 1001,  3640, 13260,  48450,  177650, ...  A115144
  [4] 0, 1, 6, 27, 110,  429, 1638,  6188, 23256,  87210,  326876, ...  A115145
  [5] 0, 1, 7, 35, 154,  637, 2548,  9996, 38760, 149226,  572033, ...  A000588
  [6] 0, 1, 8, 44, 208,  910, 3808, 15504, 62016, 245157,  961400, ...  A115147
  [7] 0, 1, 9, 54, 273, 1260, 5508, 23256, 95931, 389367, 1562275, ...  A115148
		

Crossrefs

A000108 (main diagonal), A000245 (subdiagonal), A002057 (diagonal 2), A000344 (diagonal 3), A000027 (column 2), A000096 (column 3), A071724 (row sums), A000958 (alternating row sums), A262394 (main diagonal of array).
Variants: A009766 (main variant), A030237, A130020.
Cf. A123110 (triangle of order 0), A355172 (triangle of order 2), A355174 (triangle of order 3), A355262 (Fuss-Catalan array).

Programs

  • Python
    from functools import cache
    from itertools import accumulate
    @cache
    def Trow(n: int) -> list[int]:
        if n == 0: return [1]
        if n == 1: return [0, 1]
        row = Trow(n - 1) + [Trow(n - 1)[n - 1]]
        return list(accumulate(row))
    for n in range(11): print(Trow(n))

Formula

The general formula for the Fuss-Catalan triangles is, for m >= 0 and 0 <= k <= n:
FCT(n, k, m) = (m*(n - k) + m + 1)*(m*n + k - 1)!/((m*n + 1)!*(k - 1)!) for k > 0 and FCT(n, 0, m) = 0^n. The case considered here is T(n, k) = FCT(n, k, 1).
T(n, k) = (n - k + 2)*(n + k - 1)!/((n + 1)!*(k - 1)!) for k > 0; T(n, 0) = 0^n.
The g.f. of row n of the FC-triangle of order m is 0^n + (x - (m + 1)*x^2) / (1 - x)^(m*n + 2), thus:
T(n, k) = [x^k] (0^n + (x - 2*x^2)/(1 - x)^(n + 2)).

A000913 Number of bond-rooted polyenoids with n edges.

Original entry on oeis.org

0, 1, 2, 12, 38, 143, 490, 1768, 6268, 22610, 81620, 297160, 1086172, 3991995, 14731290, 54587280, 202992808, 757398510, 2834493948, 10637507400, 40023577524, 150946230006, 570534370692, 2160865067312, 8199710635816
Offset: 1

Views

Author

E. K. Lloyd (E.K.Lloyd(AT)soton.ac.uk)

Keywords

Crossrefs

Cf. A000108 (Catalan).

Programs

  • Maple
    c:=proc(n) if floor(n)=n then binomial(2*n,n)/(n+1) else 0 fi end:a:=n->(1/4)*c(n+2)-(1/2)*c(n+1)-(3/4)*c((n+1)/2)+(1/2)*c((n-1)/4):seq(a(n),n=1..27); # Emeric Deutsch, Dec 19 2004
  • Mathematica
    c[n_] := If[Floor[n] == n, Binomial[2 n, n]/(n + 1), 0]; a[n_] := (1/4)*c[n + 2] - (1/2)*c[n + 1] - (3/4)*c[(n + 1)/2] + (1/2)*c[(n - 1)/4]; Table[a[n], {n, 1, 25}] (* James C. McMahon, Dec 09 2023 after MAPLE by Emeric Deutsch *)
  • PARI
    c(n) = if ((n<0) || (denominator(n) > 1), 0, binomial(2*n,n)/(n+1));
    a(n) = (1/4)*c(n+2) - (1/2)*c(n+1) - (3/4)*c((n+1)/2) + (1/2)*c((n-1)/4); \\ Michel Marcus, Aug 26 2019

Formula

From Emeric Deutsch, Dec 19 2004: (Start)
a(n) = (1/4)*c(n+2) - (1/2)*c(n+1) - (3/4)*c((n+1)/2) + (1/2)*c((n-1)/4), where c(n) = binomial(2n, n)/(n+1) are the Catalan numbers for n a nonnegative integer and 0 otherwise.
G.f.: (-4x + 8x^2 - sqrt(1-4x) + 2x*sqrt(1-4x) + 3*sqrt(1-4x^2) - 2*sqrt(1-4x^4))/(8x^3). (End)

Extensions

More terms from Emeric Deutsch, Dec 19 2004

A000936 Number of free planar polyenoids with n nodes and symmetry point group C_{2v}.

Original entry on oeis.org

0, 0, 1, 1, 2, 4, 4, 12, 10, 29, 27, 88, 76, 247, 217, 722, 638, 2134, 1901, 6413
Offset: 1

Views

Author

E. K. Lloyd (E.K.Lloyd(AT)soton.ac.uk)

Keywords

References

  • S. J. Cyvin, J. Brunvoll, E. Brendsdal, B. N. Cyvin and E. K. Lloyd, Enumeration of polyene hydrocarbons: a complete mathematical solution, J. Chem. Inf. Comput. Sci., 35 (1995) 743-751.

Extensions

a(16)-a(20) and title improved by Sean A. Irvine, Oct 14 2015

A000941 Number of free planar polyenoids with n nodes and symmetry point group C_s.

Original entry on oeis.org

0, 0, 0, 0, 2, 5, 21, 58, 194, 570, 1790, 5434, 16924, 52362, 163784, 512670, 1614406, 5096314, 16150180
Offset: 1

Views

Author

E. K. Lloyd (E.K.Lloyd(AT)soton.ac.uk)

Keywords

Extensions

Added a(16)-a(19) and title improved by Sean A. Irvine, Oct 13 2015

A000942 Number of free planar polyenoids with n nodes.

Original entry on oeis.org

1, 1, 1, 3, 4, 12, 26, 77, 204, 624, 1817, 5585, 17007, 52803, 164001, 514009, 1615044, 5100324, 16152134, 51324864
Offset: 1

Views

Author

E. K. Lloyd (E.K.Lloyd(AT)soton.ac.uk)

Keywords

Crossrefs

Cf. A197459 (where polyedges may have cycles).

Extensions

More terms from Sean A. Irvine, Oct 12 2015

A050163 T(n, k) = S(2n+2, n+2, k+2) for 0<=k<=n and n >= 0, array S as in A050157.

Original entry on oeis.org

1, 3, 4, 9, 14, 15, 28, 48, 55, 56, 90, 165, 200, 209, 210, 297, 572, 726, 780, 791, 792, 1001, 2002, 2639, 2912, 2989, 3002, 3003, 3432, 7072, 9620, 10880, 11320, 11424, 11439, 11440, 11934, 25194, 35190, 40698, 42942, 43605
Offset: 0

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Author

Keywords

Examples

			Triangle starts:
                                1
                              3, 4
                           9, 14, 15
                         28, 48, 55, 56
                     90, 165, 200, 209, 210
                  297, 572, 726, 780, 791, 792
            1001, 2002, 2639, 2912, 2989, 3002, 3003
		

Crossrefs

T(n, 0) = A000245(n+1).
T(n, 1) = A002057(n).
T(n, n) = A001791(n+1).
Row sums are A000531(n+1).

Programs

  • Maple
    A050163 := (n, k) -> binomial(2*n+2, n) - binomial(2*n+2, n+k+3):
    seq(seq(A050163(n,k), k=0..n), n=0..8); # Peter Luschny, Dec 21 2017

Formula

T(n, k) = Sum_{0<=j<=k} t(n, j), array t as in A050155.
T(n, k) = binomial(2*n+2, n) - binomial(2*n+2, n+k+3). - Peter Luschny, Dec 21 2017

A118920 Triangle read by rows: T(n,k) is the number of Grand Dyck paths of semilength n that cross the x-axis k times (n>=1, k>=0).

Original entry on oeis.org

2, 4, 2, 10, 8, 2, 28, 28, 12, 2, 84, 96, 54, 16, 2, 264, 330, 220, 88, 20, 2, 858, 1144, 858, 416, 130, 24, 2, 2860, 4004, 3276, 1820, 700, 180, 28, 2, 9724, 14144, 12376, 7616, 3400, 1088, 238, 32, 2, 33592, 50388, 46512, 31008, 15504, 5814, 1596, 304, 36, 2
Offset: 1

Views

Author

Emeric Deutsch, May 06 2006

Keywords

Comments

A Grand Dyck path of semilength n is a path in the half-plane x>=0, starting at (0,0), ending at (2n,0) and consisting of steps u=(1,1) and d=(1,-1).
Row sums are the central binomial coefficients (A000984). T(n,0)=2*A000108(n) (the Catalan numbers doubled). T(n,1)=2*A002057(n-2). Sum(k*T(n,k),k>=0)=2*A008549(n-1). For crossings of the x-axis in one direction, see A118919.
This triangle is related to paired pattern P_3 and P_4 defined in the Pan & Remmel link. - Ran Pan, Feb 01 2016

Examples

			T(3,1)=8 because we have ud|dudu,ud|dduu,udud|du,uudd|du,du|udud,du|uudd, dudu|ud and dduu|ud (the crossings of the x-axis are shown by |).
Triangle starts:
   2;
   4, 2;
  10, 8, 2;
  28,28,12, 2;
  84,96,54,16,2;
		

Crossrefs

Programs

  • Maple
    T:=(n,k)->2*(k+1)*binomial(2*n,n-k-1)/n: for n from 1 to 11 do seq(T(n,k),k=0..n-1) od; # yields sequence in triangular form
  • Mathematica
    Table[2 (k + 1) Binomial[2 n, n - k - 1]/n, {n, 10}, {k, 0, n - 1}] // Flatten (* Michael De Vlieger, Feb 01 2016 *)
  • PARI
    T(n,k) = 2*(k+1)*binomial(2*n,n-k-1)/n \\ Charles R Greathouse IV, Feb 01 2016
  • Sage
    # Algorithm of L. Seidel (1877)
    # Prints the first n rows of the triangle.
    def A118920_triangle(n) :
        D = [0]*(n+2); D[1] = 2
        b = True; h = 1
        for i in range(2*n) :
            if b :
                for k in range(h, 0, -1) : D[k] += D[k-1]
                h += 1
            else :
                for k in range(1, h, 1) : D[k] += D[k+1]
            b = not b
            if b : print([D[z] for z in (1..h-1)])
    A118920_triangle(10)  # Peter Luschny, Oct 19 2012
    

Formula

T(n,k) = 2*(k+1)*binomial(2*n,n-k-1)/n.
G.f.: G(t,z)=2*z*C^2/(1-t*z*C^2), where C=(1-sqrt(1-4*z))/(2*z) is the Catalan function.
More generally, the trivariate g.f. G=G(x,y,z), where x (y) marks number of downward (upward) crossings of the x-axis, is given by G = z*C^2*(2+(x+y)*z*C^2)/(1-x*y*z^2*C^4).
a(n) = 2 * A039598(n-1). - Georg Fischer, Oct 27 2021
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