A000244 -id:A000244 - cp's OEIS frontend

A005159 a(n) = 3^n*Catalan(n).

1, 3, 18, 135, 1134, 10206, 96228, 938223, 9382230, 95698746, 991787004, 10413763542, 110546105292, 1184422556700, 12791763612360, 139110429284415, 1522031755700070, 16742349312700770, 185047018719324300, 2054021907784499730

Offset: 0

N. J. A. Sloane, Valery A. Liskovets

Total number of vertices in rooted planar maps with n edges.
Number of blossom trees with n inner vertices.
The number of rooted n-edge maps in the plane (planar with a distinguished outside face). - Valery A. Liskovets, Mar 17 2005
Hankel transform is 3^(n+n^2) = A053764(n+1). - Philippe Deléham, Dec 10 2007
From Joerg Arndt, Oct 22 2012: (Start)
Also the number of strings of length 2*n of three different types of balanced parentheses.
The number of strings of length 2*n of t different types of balanced parentheses is given by t^n * A000108(n): there are n opening parentheses in the strings, giving t^n choices for the type (the closing parentheses are chosen to match). (End)
Number of Dyck paths of length 2n in which the step U=(1,1) come in 3 colors. - José Luis Ramírez Ramírez, Jan 31 2013
Number of unknown entries in bracketed Kleene's truth table connected by the implication with n distinct variables. See Yildiz link. - Michel Marcus, Oct 21 2020

Leonid M. Koganov, Valery A. Liskovets and Timothy R. S. Walsh, Total vertex enumeration in rooted planar maps, Ars Combin., Vol. 54 (2000), pp. 149-160.
Valery A. Liskovets and Timothy R. Walsh, Enumeration of unrooted maps on the plane, Rapport technique, UQAM, No. 2005-01, Montreal, Canada, 2005.
Richard P. Stanley, Catalan Numbers, Cambridge, 2015, p. 107.

T. D. Noe, Table of n, a(n) for n = 0..100
Mireille Bousquet-Mélou, Limit laws for embedded trees, arXiv:math/0501266 [math.CO], 2005.
J. Bouttier, P. Di Francesco and E. Guitter, Statistics of planar graphs viewed from a vertex: a study via labeled trees, Nucl. Phys. B, Vol. 675, No. 3 (2003), pp. 631-660. See p. 631, eq. (3.3).
Zhi Chen and Hao Pan, Identities involving weighted Catalan-Schroder and Motzkin Paths, arXiv:1608.02448 [math.CO], 2016. See eq. (1.13), a=b=3.
Aoife Hennessy, A Study of Riordan Arrays with Applications to Continued Fractions, Orthogonal Polynomials and Lattice Paths, Ph. D. Thesis, Waterford Institute of Technology, Oct. 2011.
Gerard 't Hooft, Counting planar diagrams with various restrictions, Nucl. Phys. B, Vol. 538, No. 1-2 (1999), pp. 389-410; arXiv:hep preprint arXiv:hep-th/9808113, 1998.
Hsien-Kuei Hwang, Mihyun Kang and Guan-Huei Duh, Asymptotic Expansions for Sub-Critical Lagrangean Forms, LIPIcs Proceedings of Analysis of Algorithms 2018, Vol. 110. Schloss Dagstuhl-Leibniz-Zentrum für Informatik, 2018.
Sergey Kitaev, Anna de Mier and Marc Noy, On the number of self-dual rooted maps, European J. Combin., Vol. 35 (2014), pp. 377-387. MR3090510.
Valery A. Liskovets, A pattern of asymptotic vertex valency distributions in planar maps, J. Combin. Th. B, Vol. 75, No. 1 (1999), pp. 116-133.
Valery A. Liskovets and T. R. Walsh, Counting unrooted maps on the plane, Advances in Applied Math., Vol. 36, No. 4 (2006), pp. 364-387.
Thomas M. Richardson, The three 'R's and Dual Riordan Arrays, arXiv:1609.01193 [math.CO], 2016.
Gilles Schaeffer and Paul Zinn-Justin, On the asymptotic number of plane curves and alternating knots, arXiv:math-ph/0304034, 2003-2004.
Simeon T. Stefanov, Counting fixed points free vector fields on B^2, arXiv:1807.03714 [math.GT], 2018.
Volkan Yildiz, Counting with 3-valued truth tables of bracketed formulae connected by implication, arXiv:2010.10303 [math.GM], 2020.

Cf. A000108, A000244, A025226, A053764, A085880.

Limit of array A102994.

List([0..20],n->3^n*Binomial(2*n,n)/(n+1)); # Muniru A Asiru, Mar 30 2018

[3^n*Catalan(n): n in [0..20]]; // Vincenzo Librandi, Oct 16 2018

A005159_list := proc(n) local j, a, w; a := array(0..n); a[0] := 1;
for w from 1 to n do a[w] := 3*(a[w-1]+add(a[j]*a[w-j-1],j=1..w-1)) od;convert(a,list)end: A005159_list(19); # Peter Luschny, May 19 2011

InverseSeries[Series[y-3*y^2, {y, 0, 24}], x] (* then A(x)=y(x)/x *) (* Len Smiley, Apr 07 2000 *)
Table[3^n CatalanNumber[n],{n,0,30}] (* Harvey P. Dale, May 18 2011 *)
CoefficientList[Series[(1 - Sqrt[1-4*(3*x)])/(6*x), {x, 0, 50}], x] (* Stefano Spezia, Oct 16 2018 *)

a(n) = 3^n*binomial(2*n,n)/(n+1) \\ Charles R Greathouse IV, Feb 06 2017

G.f.: 2/(1+sqrt(1-12x)) = (1 - sqrt(1-4*(3*x))) / (6*x).
With offset 1 : a(1)=1, a(n) = 3*Sum_{i=1..n-1} a(i)*a(n-i). - Benoit Cloitre, Mar 16 2004
G.f.: c(3*x) with c(x) the o.g.f. of A000108 (Catalan).
From Gary W. Adamson, Jul 12 2011: (Start)
a(n) is the upper left term in M^n, M = the infinite square production matrix:
  3, 3, 0, 0, 0, 0, ...
  3, 3, 3, 0, 0, 0, ...
  3, 3, 3, 3, 0, 0, ...
  3, 3, 3, 3, 3, 0, ...
  3, 3, 3, 3, 3, 3, ...
  ... (End)
D-finite with recurrence (n+1)*a(n)+6*(1-2n)*a(n-1)=0. - R. J. Mathar, Apr 01 2012
E.g.f.: a(n) = n!* [x^n] KummerM(1/2, 2, 12*x). - Peter Luschny, Aug 25 2012
a(n) = sum_{k=0..n} A085880(n,k)*2^k. - Philippe Deléham, Nov 15 2013
From Ilya Gutkovskiy, Dec 04 2016: (Start)
E.g.f.: (BesselI(0,6*x) - BesselI(1,6*x))*exp(6*x).
a(n) ~ 12^n/(sqrt(Pi)*n^(3/2)). (End)
a(n) = A000244(n)*A000108(n). - Omar E. Pol, Mar 30 2018
Sum_{n>=0} 1/a(n) = 150/121 + 216*arctan(1/sqrt(11)) / (121*sqrt(11)). - Vaclav Kotesovec, Nov 23 2021
Sum_{n>=0} (-1)^n/a(n) = 138/169 - 216*arctanh(1/sqrt(13)) / (169*sqrt(13)). - Amiram Eldar, Jan 25 2022
G.f.: 1/(1-3*x/(1-3*x/(1-3*x/(1-3*x/(1-3*x/(1-3*x/(1-3*x/(1-3*x/(1-...))))))))) (continued fraction). - Nikolaos Pantelidis, Nov 20 2022

A020914 Number of digits in the base-2 representation of 3^n.

Original entry on oeis.org

1, 2, 4, 5, 7, 8, 10, 12, 13, 15, 16, 18, 20, 21, 23, 24, 26, 27, 29, 31, 32, 34, 35, 37, 39, 40, 42, 43, 45, 46, 48, 50, 51, 53, 54, 56, 58, 59, 61, 62, 64, 65, 67, 69, 70, 72, 73, 75, 77, 78, 80, 81, 83, 85, 86, 88, 89, 91, 92, 94, 96, 97, 99, 100, 102, 104, 105, 107

Offset: 0

Clark Kimberling

Also, numbers k such that the first digit in the ternary expansion of 2^k is 1. - Mohammed Bouayoun (Mohammed.bouayoun(AT)sanef.com), Apr 24 2006
a(n) is the smallest integer such that n/a(n) < log_2(3). - Trevor G. Hyde (thyde12(AT)amherst.edu), Jul 31 2008
This sequence represents allowable values of the "dropping time" in the Collatz (3x+1) problem when iterated according to the function f(n) := n/2 if n is even, (3n+1)/2 otherwise, as tabulated in A126241. There is one exception, A126241(1), which has been set to zero by convention. - K. Spage, Oct 22 2009
An integer k is a term of A020914 if and only if floor(k*(1 + log(2)/log(3))) - abs(k-1)*(1 + log(2)/log(3)) - 1 >= 0. - K. Spage, Oct 22 2009
Also smallest k such that ceiling(2^k / 3^n) = 2. - Michel Lagneau, Jan 31 2012
For n > 0, first differences of A022330. - Michel Marcus, Oct 03 2013
Also the number of powers of two less than or equal to 3^n. - Robert G. Wilson v, May 25 2014
Except for 1, A020914 is the complement of A054414 and therefore these two form a pair of Beatty sequences. - Robert G. Wilson v, May 25 2014

T. D. Noe, R. J. Mathar, Table of n, a(n) for n = 0..20000
Mike Winkler, On the structure and the behaviour of Collatz 3n + 1 sequences, 2014.
Mike Winkler, New results on the stopping time behaviour of the Collatz 3x + 1 function, arXiv:1504.00212 [math.GM], 2015.
Mike Winkler, The algorithmic structure of the finite stopping time behavior of the 3x + 1 function, arXiv:1709.03385 [math.GM], 2017.

Cf. A056576, A054414, A070939, A000244, A227048, A022330, A022921 (first differences), A126241.
Cf. A020857 (decimal expansion of log_2(3)).
Cf. A020915.
Cf. A204399 (essentially the same).

a020914 = a070939 . a000244  -- Reinhard Zumkeller, Jun 30 2013

A020914 :=n->nops(convert(3^n,base,2)):
seq(A020914(n),n=0..70); # Emeric Deutsch, Apr 30 2006
seq(ilog2(3^n)+1, n=0 .. 100); # Robert Israel, Dec 12 2014

Table[Length[IntegerDigits[3^n, 2]], {n, 0, 100}] (* Stefan Steinerberger, Apr 19 2006 *)
a[n_] := Floor[ Log2[3^n] + 1]; Array[a, 105, 0] (* Robert G. Wilson v, May 25 2014 *)

for(n=0,100,print1(floor(1+n*log(3)/log(2)),",")) \\ K. Spage, Oct 22 2009

a(n)=exponent(3^n)+1 \\ Charles R Greathouse IV, Nov 03 2022

def A020914(n): return (3**n).bit_length() # Chai Wah Wu, Oct 09 2024

a(n) = floor(1 + n*log(3)/log(2)). - K. Spage, Oct 22 2009
a(0) = 1, a(n+1) = a(n) + A022921(n). - K. Spage, Oct 23 2009
a(n) = A122437(n-1) - n. - K. Spage, Oct 23 2009
A098294(n) = a(n) + n for n > 0. - Mike Winkler, Dec 31 2010
a(n) = A070939(A000244(n)) = length of n-th row in triangle A227048. - Reinhard Zumkeller, Jun 30 2013
a(n) = 1 + floor(n*log_2(3)) = 1 + A056576(n) = 1 + floor(n*A020857). - L. Edson Jeffery, Dec 12 2014
A020915(a(n)) = n + 1. - Reinhard Zumkeller, Mar 28 2015

More terms from Stefan Steinerberger, Apr 19 2006

A062153 a(n) = floor(log_3(n)).

Original entry on oeis.org

0, 0, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4

Offset: 1

Henry Bottomley, Jun 06 2001

Harry J. Smith, Table of n, a(n) for n = 1..1000

Cf. A000244, A000523, A007089, A102572.

[ Ilog(3,n) : n in [1..100] ]; // N. J. A. Sloane, Dec 23 2006

Floor[Log[3,Range[120]]]  (* Harvey P. Dale, Apr 30 2011 *)

a(n)=logint(n,3) \\ Charles R Greathouse IV, Nov 15 2022

a(n) = (number of digits of n when written in base 3) - 1.
a(n) = if n > 2 then a(floor(n / 3)) + 1 else 0. - Reinhard Zumkeller, Oct 29 2001
G.f.: (1/(1 - x))*Sum_{k>=1} x^(3^k). - Ilya Gutkovskiy, Jan 08 2017

A285280 Array read by antidiagonals: T(m,n) = number of m-ary words of length n with cyclically adjacent elements differing by 2 or less.

Original entry on oeis.org

1, 3, 1, 9, 4, 1, 27, 14, 5, 1, 81, 46, 19, 6, 1, 243, 162, 65, 24, 7, 1, 729, 574, 247, 84, 29, 8, 1, 2187, 2042, 955, 332, 103, 34, 9, 1, 6561, 7270, 3733, 1336, 417, 122, 39, 10, 1, 19683, 25890, 14649, 5478, 1717, 502, 141, 44, 11, 1

Offset: 3

Andrew Howroyd, Apr 15 2017

All rows are linear recurrences with constant coefficients. See PARI script to obtain generating functions.

			Table starts (m>=3, n>=0):
1  3  9  27  81  243   729  2187 ...
1  4 14  46 162  574  2042  7270 ...
1  5 19  65 247  955  3733 14649 ...
1  6 24  84 332 1336  5478 22658 ...
1  7 29 103 417 1717  7229 30793 ...
1  8 34 122 502 2098  8980 38928 ...
1  9 39 141 587 2479 10731 47063 ...
1 10 44 160 672 2860 12482 55198 ...

Andrew Howroyd, Table of n, a(n) for n = 3..1277

Rows 3-32 are A000244, A124805, A124806, A124807, A124828, A124843, A124851, A124852, A124857, A124858, A124864, A124892-A124894, A124898, A124935, A124947, A124948-A124958, A124994, A124998.

Cf. A285266, A276562, A285281.

diff = 2; m0 = diff + 1; mmax = 12;
TransferGf[m_, u_, t_, v_, z_] := Array[u, m].LinearSolve[IdentityMatrix[m] - z*Array[t, {m, m}], Array[v, m]]
RowGf[d_, m_, z_] := 1 + z*Sum[TransferGf[m, Boole[# == k] &, Boole[Abs[#1 - #2] <= d] &, Boole[Abs[# - k] <= d] &, z], {k, 1, m}];
row[m_] := row[m] = CoefficientList[RowGf[diff, m, x] + O[x]^mmax, x];
T[m_ /; m >= m0, n_ /; n >= 0] := row[m][[n + 1]];
Table[T[m - n, n], {m, m0, mmax}, {n, m - m0, 0, -1}] // Flatten (* Jean-François Alcover, Jun 16 2017, adapted from PARI *)

TransferGf(m,u,t,v,z)=vector(m,i,u(i))*matsolve(matid(m)-z*matrix(m,m,i,j,t(i,j)),vectorv(m,i,v(i)));
RowGf(d,m,z)=1+z*sum(k=1,m,TransferGf(m, i->if(i==k,1,0), (i,j)->abs(i-j)<=d, j->if(abs(j-k)<=d,1,0), z));
for(m=3, 10, print(RowGf(2,m,x)));
for(m=3, 10, v=Vec(RowGf(2,m,x) + O(x^8)); for(n=1, length(v), print1( v[n], ", ") ); print(); );

A000340 a(0)=1, a(n) = 3*a(n-1) + n + 1.

Original entry on oeis.org

1, 5, 18, 58, 179, 543, 1636, 4916, 14757, 44281, 132854, 398574, 1195735, 3587219, 10761672, 32285032, 96855113, 290565357, 871696090, 2615088290, 7845264891, 23535794695, 70607384108, 211822152348, 635466457069

Offset: 0

N. J. A. Sloane, Simon Plouffe

From Johannes W. Meijer, Feb 20 2009: (Start)
Second right hand column (n-m=1) of the A156920 triangle.
The generating function of this sequence enabled the analysis of the polynomials A156921 and A156925.
(End)
Partial sums of A003462, and thus the second partial sums of A000244 (3^n). Also column k=2 of A106516. - John Keith, Jan 04 2022

			G.f. = 1 + 5*x + 18*x^2 + 58*x^3 + 179*x^4 + 543*x^5 + 1636*x^6 + ...

F. N. David, M. G. Kendall and D. E. Barton, Symmetric Function and Allied Tables, Cambridge, 1966, p. 260.
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).

Vincenzo Librandi, Table of n, a(n) for n = 0..1000
Dillan Agrawal, Selena Ge, Jate Greene, Tanya Khovanova, Dohun Kim, Rajarshi Mandal, Tanish Parida, Anirudh Pulugurtha, Gordon Redwine, Soham Samanta, and Albert Xu, Chip-Firing on Infinite k-ary Trees, arXiv:2501.06675 [math.CO], 2025. See pp. 9, 18.
Shaoshi Chen, Hanqian Fang, Sergey Kitaev, and Candice X.T. Zhang, Patterns in Multi-dimensional Permutations, arXiv:2411.02897 [math.CO], 2024. See p. 7.
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 389
Simon Plouffe, Approximations de séries génératrices et quelques conjectures, Dissertation, Université du Québec à Montréal, 1992; arXiv:0911.4975 [math.NT], 2009.
Simon Plouffe, 1031 Generating Functions, Appendix to Thesis, Montreal, 1992
László Tóth, On Schizophrenic Patterns in b-ary Expansions of Some Irrational Numbers, arXiv:2002.06584 [math.NT], 2020. Mentions this sequence. See also Proc. Amer. Math. Soc. 148 (2020), 461-469.
Index entries for linear recurrences with constant coefficients, signature (5,-7,3).

From Johannes W. Meijer, Feb 20 2009: (Start)
Cf. A156921, A156925, A156927, A156933. Other columns A156922, A156923, A156924.
Equals A156920 second right hand column.
Equals A142963 second right hand column divided by 2^n.
Equals A156919 second right hand column divided by 2.
(End)
Cf. A014915.
Equals column k=1 of A008971 (shifted). - Jeremy Dover, Jul 11 2021
Cf. A000340, A003462 (first differences), A106516.

[(3^(n+2)-2*n-5)/4: n in [0..30]]; // Vincenzo Librandi, Aug 15 2011

a[ -1]:=0:a[0]:=1:for n from 1 to 50 do a[n]:=4*a[n-1]-3*a[n-2]+1 od: seq(a[n],n=0..50); # Miklos Kristof, Mar 09 2005
A000340:=-1/(3*z-1)/(z-1)**2; # conjectured by Simon Plouffe in his 1992 dissertation

a[ n_] := MatrixPower[ {{1, 0, 0}, {1, 1, 0}, {1, 1, 3}}, n + 1][[3, 1]]; (* Michael Somos, May 28 2014 *)
RecurrenceTable[{a[0]==1,a[n]==3a[n-1]+n+1},a,{n,30}] (* or *) LinearRecurrence[{5,-7,3},{1,5,18},30] (* Harvey P. Dale, Jan 31 2017 *)

G.f.: 1/((1-3*x)*(1-x)^2).
a(n) = (3^(n+2) - 2*n - 5)/4.
a(n) = Sum_{k=0..n+1} (n-k+1)*3^k = Sum_{k=0..n+1} k*3^(n-k+1). - Paul Barry, Jul 30 2004
a(n) = Sum_{k=0..n} binomial(n+2, k+2)*2^k. - Paul Barry, Jul 30 2004
a(-1)=0, a(0)=1, a(n) = 4*a(n-1) - 3*a(n-2) + 1. - Miklos Kristof, Mar 09 2005
a(n) = 5*a(n-1) - 7*a(n-2) + 3*a(n-3). - Johannes W. Meijer, Feb 20 2009
a(-2 - n) = 3^-n * A014915(n). - Michael Somos, May 28 2014
E.g.f.: exp(x)*(9*exp(2*x) - 2*x - 5)/4. - Stefano Spezia, Nov 09 2024

A175654 Eight bishops and one elephant on a 3 X 3 chessboard. G.f.: (1 - x - x^2)/(1 - 3x - x^2 + 6x^3).

Original entry on oeis.org

1, 2, 6, 14, 36, 86, 210, 500, 1194, 2822, 6660, 15638, 36642, 85604, 199626, 464630, 1079892, 2506550, 5811762, 13462484, 31159914, 72071654, 166599972, 384912086, 888906306, 2052031172, 4735527306, 10925175254, 25198866036, 58108609526, 133973643090

Offset: 0

Johannes W. Meijer, Aug 06 2010; edited Jun 21 2013

a(n) represents the number of n-move routes of a fairy chess piece starting in a given corner square (m = 1, 3, 7 or 9) on a 3 X 3 chessboard. This fairy chess piece behaves like a bishop on the eight side and corner squares but on the center square the bishop flies into a rage and turns into a raging elephant.
In chaturanga, the old Indian version of chess, one of the pieces was called gaja, elephant in Sanskrit. The Arabs called the game shatranj and the elephant became el fil in Arabic. In Spain chess became chess as we know it today but surprisingly in Spanish a bishop isn't a Christian bishop but a Moorish elephant and it still goes by its original name of el alfil.
On a 3 X 3 chessboard there are 2^9 = 512 ways for an elephant to fly into a rage on the central square (off the center the piece behaves like a normal bishop). The elephant is represented by the A[5] vector in the fifth row of the adjacency matrix A, see the Maple program and A180140. For the corner squares the 512 elephants lead to 46 different elephant sequences, see the overview of elephant sequences and the crossreferences.
The sequence above corresponds to 16 A[5] vectors with decimal values 71, 77, 101, 197, 263, 269, 293, 323, 326, 329, 332, 353, 356, 389, 449 and 452. These vectors lead for the side squares to A000079 and for the central square to A175655.

Gary Chartrand, Introductory Graph Theory, pp. 217-221, 1984.
David Hooper and Kenneth Whyld, The Oxford Companion to Chess, pp. 74, 366, 1992.

Vincenzo Librandi, Table of n, a(n) for n = 0..1000
Viswanathan Anand, The Indian Defense, Time, Jun 19 2008.
Vladimir Kruchinin, Composition of ordinary generating functions, arXiv:1009.2565 [math.CO], 2010.
Johannes W. Meijer, The elephant sequences.
Wikipedia, War Elephant.
Index entries for linear recurrences with constant coefficients, signature (3,1,-6).

Cf. Elephant sequences corner squares [decimal value A[5]]: A040000 [0], A000027 [16], A000045 [1], A094373 [2], A000079 [3], A083329 [42], A027934 [11], A172481 [7], A006138 [69], A000325 [26], A045623 [19], A000129 [21], A095121 [170], A074878 [43], A059570 [15], A175654 [71, this sequence], A026597 [325], A097813 [58], A057711 [27], 2*A094723 [23; n>=-1], A002605 [85], A175660 [171], A123203 [186], A066373 [59], A015518 [341], A134401 [187], A093833 [343].

Cf. A000244, A006130, A006138, A075188, A175655, A180140.

[n le 3 select Factorial(n) else 3*Self(n-1) +Self(n-2) -6*Self(n-3): n in [1..41]]; // G. C. Greubel, Dec 08 2021

nmax:=28; m:=1; A[1]:=[0,0,0,0,1,0,0,0,1]: A[2]:=[0,0,0,1,0,1,0,0,0]: A[3]:=[0,0,0,0,1,0,1,0,0]: A[4]:=[0,1,0,0,0,0,0,1,0]: A[5]:=[0,0,1,0,0,0,1,1,1]: A[6]:=[0,1,0,0,0,0,0,1,0]: A[7]:=[0,0,1,0,1,0,0,0,0]: A[8]:=[0,0,0,1,0,1,0,0,0]: A[9]:=[1,0,0,0,1,0,0,0,0]: A:=Matrix([A[1], A[2], A[3], A[4], A[5], A[6], A[7], A[8], A[9]]): for n from 0 to nmax do B(n):=A^n: a(n):= add(B(n)[m,k],k=1..9): od: seq(a(n), n=0..nmax);

LinearRecurrence[{3,1,-6}, {1,2,6}, 80] (* Vladimir Joseph Stephan Orlovsky, Feb 21 2012 *)

a(n)=([0,1,0; 0,0,1; -6,1,3]^n*[1;2;6])[1,1] \\ Charles R Greathouse IV, Oct 03 2016

[( (1-x-x^2)/((1-2*x)*(1-x-3*x^2)) ).series(x,n+1).list()[n] for n in (0..40)] # G. C. Greubel, Dec 08 2021

G.f.: (1 - x - x^2)/(1 - 3*x - x^2 + 6*x^3).
a(n) = 3*a(n-1) + a(n-2) - 6*a(n-3) with a(0)=1, a(1)=2 and a(2)=6.
a(n) = ((6+10*A)*A^(-n-1) + (6+10*B)*B^(-n-1))/13 - 2^n with A = (-1+sqrt(13))/6 and B = (-1-sqrt(13))/6.
Limit_{k->oo} a(n+k)/a(k) = (-1)^(n)*2*A000244(n)/(A075118(n) - A006130(n-1)*sqrt(13)).
a(n) = b(n) - b(n-1) - b(n-2), where b(n) = Sum_{k=1..n} Sum_{j=0..k} binomial(j,n-3*k+2*j)*(-6)^(k-j)*binomial(k,j)*3^(3*k-n-j), n>0, b(0)=1, with a(0) = b(0), a(1) = b(1) - b(0). - Vladimir Kruchinin, Aug 20 2010
a(n) = 2*A006138(n) - 2^n = 2*(A006130(n) + A006130(n-1)) - 2^n. - G. C. Greubel, Dec 08 2021
E.g.f.: 2*exp(x/2)*(13*cosh(sqrt(13)*x/2) + 3*sqrt(13)*sinh(sqrt(13)*x/2))/13 - cosh(2*x) - sinh(2*x). - Stefano Spezia, Feb 12 2023

A058481 a(n) = 3^n - 2.

Original entry on oeis.org

1, 7, 25, 79, 241, 727, 2185, 6559, 19681, 59047, 177145, 531439, 1594321, 4782967, 14348905, 43046719, 129140161, 387420487, 1162261465, 3486784399, 10460353201, 31381059607, 94143178825, 282429536479, 847288609441

Offset: 1

Vladeta Jovovic, Nov 26 2000

a(n) = number of 2 X n binary matrices with no zero rows or columns.
a(n)^2 + 2*a(n+1) + 1 is a square number, i.e., a(n)^2 + 2*a(n+1) + 1 = (a(n)+3)^2: for n=2, a(2)^2 + 2*a(3) + 1 = 7^2 + 2*25 + 1 = 100 = (7+3)^2; for n=3, a(3)^2 + 2*a(4) + 1 = 25^2 + 2*79 + 1 = 784 = (25+3)^2. - Bruno Berselli, Apr 23 2010
Sum of n-th row of triangle of powers of 3: 1; 3 1 3; 9 3 1 3 9; 27 9 3 1 3 9 27; ... . - Philippe Deléham, Feb 24 2014
a(n) = least k such that k*3^n + 1 is a square. Thus, the square is given by (3^n-1)^2. - Derek Orr, Mar 23 2014
Binomial transform of A058481: (1, 6, 12, 24, 48, 96, ...) and second binomial transform of (1, 5, 1, 5, 1, 5, ...). - Gary W. Adamson, Aug 24 2016
Number of ordered pairs of nonempty sets whose union is [n]. a(2) = 7: ({1,2},{1,2}), ({1,2},{1}), ({1,2},{2}), ({1},{1,2}), ({1},{2}), ({2},{1,2}), ({2},{1}). If "nonempty" is omitted we get A000244. - Manfred Boergens, Mar 29 2023

			G.f. = x + 7*x^2 + 25*x^3 + 79*x^4 + 241*x^5 + 727*x^6 + 2185*x^7 + 6559*x^8 + ...
a(1) = 1;
a(2) = 3 + 1 + 3 = 7;
a(3) = 9 + 3 + 1 + 3 + 9 = 25;
a(4) = 27 + 9 + 3 + 1 + 3 + 9 + 27 = 79; etc. - _Philippe Deléham_, Feb 24 2014

G. C. Greubel, Table of n, a(n) for n = 1..1000
John Elias, Illustration: Union of Triple-Sierpinski Triangles
Index entries for linear recurrences with constant coefficients, signature (4,-3).

Cf. A055602, A024206 (unlabeled case), A055609, A058482, A000244.

Cf. A003462, A007051, A034472, A024023, A067771, A029858, A134931, A115099, A100774, A079004.

A058481:=n->3^n-2; seq(A058481(n), n=1..30); # Wesley Ivan Hurt, Mar 24 2014

a=1;lst={a};Do[a=a*3+4;AppendTo[lst,a],{n,0,5!}];lst (* Vladimir Joseph Stephan Orlovsky, Dec 25 2008 *)
3^Range[30]-2  (* Harvey P. Dale, Mar 28 2011 *)
LinearRecurrence[{4, -3}, {1, 7}, 25] (* G. C. Greubel, Aug 25 2016 *)

a(n)=3^n-2 \\ Charles R Greathouse IV, Feb 06 2017

{a(n) = if( n<1, 0, 3^n - 2)}; /* Michael Somos, Feb 17 2017 */

Number of m X n binary matrices with no zero rows or columns is Sum_{j=0..m} (-1)^j*C(m, j)*(2^(m-j)-1)^n.
From Mohammad K. Azarian, Jan 14 2009: (Start)
G.f.: 1/(1-3*x)-2/(1-x)+1.
E.g.f.: e^(3*x)-2*(e^x)+1. (End)
a(n) = 3*a(n-1) + 4 (with a(1)=1). - Vincenzo Librandi, Aug 07 2010
a(n) = 4*a(n-1) - 3*a(n-2). - G. C. Greubel, Aug 25 2016

More terms from Larry Reeves (larryr(AT)acm.org), Dec 04 2000

A013708 a(n) = 3^(2*n+1).

Original entry on oeis.org

3, 27, 243, 2187, 19683, 177147, 1594323, 14348907, 129140163, 1162261467, 10460353203, 94143178827, 847288609443, 7625597484987, 68630377364883, 617673396283947, 5559060566555523, 50031545098999707, 450283905890997363, 4052555153018976267, 36472996377170786403

Offset: 0

N. J. A. Sloane

1/3 + 1/27 + 1/243 + ... = 3/8. - Gary W. Adamson, Aug 29 2008

Number k such that if a=k, b=8*k, c=15*k, d=36*k*sqrt(3*k), then a^3 + b^3 + c^3 = d^2; e.g.: a=3, b=24, c=45, d=324, 3^3 + 24^3 + 45^3 = 324^2. - Vincenzo Librandi, Nov 20 2010

Delbert L. Johnson, Table of n, a(n) for n = 0..1047
Tanya Khovanova, Recursive Sequences.
R. J. Mathar, Counting Walks on Finite Graphs, Nov 2020, Section 4.
Index entries for linear recurrences with constant coefficients, signature (9).

Cf. A000244.

NestList[9#&,3,20] (* Harvey P. Dale, Apr 21 2014 *)

a(n)=3^(2*n+1) \\ Charles R Greathouse IV, Aug 05 2015

print([3**(2*n+1) for n in range(18)]) # Michael S. Branicky, Mar 27 2021

From Philippe Deléham, Nov 23 2008: (Start)
a(n) = 9*a(n-1), n > 0; a(0)=3.
G.f.: 3/(1-9*x). (End)
a(n) = A000244(2*n+1). - R. J. Mathar, Jul 10 2015
E.g.f.: 3*exp(9*x). - Stefano Spezia, Jul 09 2024

A303401 Number of ways to write n as a(3a-1)/2 + b(3b-1)/2 + 3^c + 3^d with a,b,c,d nonnegative integers.

Original entry on oeis.org

0, 1, 1, 2, 1, 2, 2, 2, 1, 2, 2, 4, 1, 3, 2, 3, 2, 3, 3, 2, 1, 2, 3, 3, 2, 2, 2, 4, 4, 4, 3, 2, 3, 3, 3, 4, 3, 4, 2, 5, 4, 5, 1, 2, 3, 5, 2, 3, 2, 3, 2, 4, 5, 5, 3, 3, 3, 4, 4, 3, 2, 4, 4, 4, 3, 3, 3, 2, 3, 3, 2, 4, 2, 4, 5, 4, 5, 1, 3, 4

Offset: 1

Zhi-Wei Sun, Apr 23 2018

nonn

Conjecture: a(n) > 0 for all n > 1. In other words, any integer n > 1 can be written as the sum of two pentagonal numbers and two powers of 3.

a(n) > 0 for all n = 2..7*10^6. See A303434 for the numbers of the form x*(3*x-1)/2 + 3^y with x and y nonnegative integers. See also A303389 and A303432 for similar conjectures.

Zhi-Wei Sun, Table of n, a(n) for n = 1..10000
Zhi-Wei Sun, On universal sums of polygonal numbers, Sci. China Math. 58(2015), no. 7, 1367-1396.
Zhi-Wei Sun, Refining Lagrange's four-square theorem, J. Number Theory 175(2017), 167-190.
Zhi-Wei Sun, New conjectures on representations of integers (I), Nanjing Univ. J. Math. Biquarterly 34(2017), no. 2, 97-120.

Cf. A000244, A000326, A303233, A303338, A303363, A303389, A303393, A303399, A303428, A303432, A303434.

SQ[n_]:=SQ[n]=IntegerQ[Sqrt[n]];
PenQ[n_]:=PenQ[n]=SQ[24n+1]&&(n==0||Mod[Sqrt[24n+1]+1,6]==0);
f[n_]:=f[n]=FactorInteger[n];
g[n_]:=g[n]=Sum[Boole[Mod[Part[Part[f[n],i],1],4]==3&&Mod[Part[Part[f[n],i],2],2]==1],{i,1,Length[f[n]]}]==0;
QQ[n_]:=QQ[n]=(n==0)||(n>0&&g[n]);
tab={};Do[r=0;Do[If[QQ[12(n-3^j-3^k)+1],Do[If[PenQ[n-3^j-3^k-x(3x-1)/2],r=r+1],{x,0,(Sqrt[12(n-3^j-3^k)+1]+1)/6}]],{j,0,Log[3,n/2]},{k,j,Log[3,n-3^j]}];tab=Append[tab,r],{n,1,80}];Print[tab]

a(78) = 1 with 78 = 3*(3*3-1)/2 + 3*(3*3-1)/2 + 3^3 + 3^3.
a(285) = 1 with 285 = 3*(3*1-1)/2 + 11*(3*11-1)/2 + 3^3 + 3^4.
a(711) = 1 with 711 = 9*(3*9-1)/2 + 20*(3*20-1)/2 + 3^0 + 3^1.
a(775) = 1 with 775 = 7*(3*7-1)/2 + 21*(3*21-1)/2 + 3^3 + 3^3.
a(3200) = 1 with 12*(3*12-1)/2 + 44*(3*44-1)/2 + 3^3 + 3^4.
a(13372) = 1 with 13372 = 17*(3*17-1)/2 + 65*(3*65-1)/2 + 3^4 + 3^8.
a(16545) = 1 with 16545 = 0*(3*0-1)/2 + 98*(3*98-1)/2 + 3^0 + 3^7.

A004166 Sum of digits of 3^n.

Original entry on oeis.org

1, 3, 9, 9, 9, 9, 18, 18, 18, 27, 27, 27, 18, 27, 45, 36, 27, 27, 45, 36, 45, 27, 45, 54, 54, 63, 63, 81, 72, 72, 63, 81, 63, 72, 99, 81, 81, 90, 90, 81, 90, 99, 90, 108, 90, 99, 108, 126, 117, 108, 144, 117, 117, 135, 108, 90, 90, 108, 126, 117, 99

Offset: 0

N. J. A. Sloane

All terms a(n), n > 1, are divisible by 9. - M. F. Hasler, Sep 27 2017

Michel Marcus, Table of n, a(n) for n = 0..10000 (terms 0..1000 from Vincenzo Librandi)
Albert Frank, Solutions of International Contest Of Logical Sequences, 2002 - 2003. (The original Contest page without solutions was removed but remains available on web.archive.org.)

Cf. A067500, A118872, A175435.

Cf. sum of digits of k^n: A001370 (k=2), this sequence (k=3), A065713 (k=4), A066001 (k=5), A066002 (k=6), A066003 (k=7), A066004 (k=8), A065999 (k=9), A066005 (k=11), A066006 (k=12), A175527 (k=13).

Total[IntegerDigits[#]]&/@(3^Range[0,60]) (* Harvey P. Dale, Mar 03 2013 *)
Table[Total[IntegerDigits[3^n]], {n, 0, 60}] (* Vincenzo Librandi, Oct 08 2013 *)

a(n)=sumdigits(3^n); \\ Michel Marcus, Nov 01 2013

def a(n): return sum(map(int, str(3**n)))
print([a(n) for n in range(61)]) # Michael S. Branicky, Apr 25 2022

a(n) = A007953(A000244(n)). - Michel Marcus, Nov 01 2013

Edited by M. F. Hasler, May 18 2017

cp's OEIS Frontend

A005159 a(n) = 3^n*Catalan(n).

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A020914 Number of digits in the base-2 representation of 3^n.

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A062153 a(n) = floor(log_3(n)).

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A285280 Array read by antidiagonals: T(m,n) = number of m-ary words of length n with cyclically adjacent elements differing by 2 or less.

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A000340 a(0)=1, a(n) = 3*a(n-1) + n + 1.

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A175654 Eight bishops and one elephant on a 3 X 3 chessboard. G.f.: (1 - x - x^2)/(1 - 3*x - x^2 + 6*x^3).

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A175654 Eight bishops and one elephant on a 3 X 3 chessboard. G.f.: (1 - x - x^2)/(1 - 3x - x^2 + 6x^3).

A303401 Number of ways to write n as a(3a-1)/2 + b(3b-1)/2 + 3^c + 3^d with a,b,c,d nonnegative integers.