A015128 -id:A015128 - cp's OEIS frontend

A211970 Square array read by antidiagonal: T(n,k), n >= 0, k >= 0, which arises from a generalization of Euler's Pentagonal Number Theorem.

1, 1, 1, 2, 1, 1, 4, 2, 1, 1, 6, 3, 1, 1, 1, 10, 5, 2, 1, 1, 1, 16, 7, 3, 1, 1, 1, 1, 24, 11, 4, 2, 1, 1, 1, 1, 36, 15, 5, 3, 1, 1, 1, 1, 1, 54, 22, 7, 4, 2, 1, 1, 1, 1, 1, 78, 30, 10, 4, 3, 1, 1, 1, 1, 1, 1, 112, 42, 13, 5, 4, 2, 1, 1, 1, 1, 1, 1

Offset: 0

Omar E. Pol, Jun 10 2012

In the infinite square array if k is positive then column k is related to the generalized m-gonal numbers, where m = k+4. For example: column 1 is related to the generalized pentagonal numbers A001318. Column 2 is related to the generalized hexagonal numbers A000217 (note that A000217 is also the entry for the triangular numbers). And so on...
In the following table Euler's Pentagonal Number Theorem is represented by the entries A001318, A195310, A175003 and A000041. It seems unusual that the partition numbers are located in a middle column (see below row 1 of the table):
========================================================
.                                          Column k of
.                                          this square
.       Generalized   Triangle  Triangle   array A211970
k    m    m-gonal       "A"       "B"      [row sums of
.         numbers                          triangle "B"
.        (if k>=1)                         with a(0)=1,
.                                          if k >= 0]
========================================================
0    4    A008794        -         -         A211971
1    5    A001318     A195310   A175003      A000041
2    6    A000217     A195826   A195836      A006950
3    7    A085787     A195827   A195837      A036820
4    8    A001082     A195828   A195838      A195848
5    9    A118277     A195829   A195839      A195849
6   10    A074377     A195830   A195840      A195850
7   11    A195160     A195831   A195841      A195851
8   12    A195162     A195832   A195842      A195852
9   13    A195313     A195833   A195843      A196933
10  14    A195818     A210944   A210954      A210964
...
It appears that column 2 of the square array is A006950.
It appears that column 3 of the square array is A036820.
The partial sums of column 0 give A015128. - Omar E. Pol, Feb 09 2014

			Array begins:
1,     1,   1,   1,   1,   1,  1,  1,  1,  1,  1, ...
1,     1,   1,   1,   1,   1,  1,  1,  1,  1,  1, ...
2,     2,   1,   1,   1,   1,  1,  1,  1,  1,  1, ...
4,     3,   2,   1,   1,   1,  1,  1,  1,  1,  1, ...
6,     5,   3,   2,   1,   1,  1,  1,  1,  1,  1, ...
10,    7,   4,   3,   2,   1,  1,  1,  1,  1,  1, ...
16,   11,   5,   4,   3,   2,  1,  1,  1,  1,  1, ...
24,   15,   7,   4,   4,   3,  2,  1,  1,  1,  1, ...
36,   22,  10,   5,   4,   4,  3,  2,  1,  1,  1, ...
54,   30,  13,   7,   4,   4,  4,  3,  2,  1,  1, ...
78,   42,  16,  10,   5,   4,  4,  4,  3,  2,  1, ...
112,  56,  21,  12,   7,   4,  4,  4,  4,  3,  2, ...
160,  77,  28,  14,  10,   5,  4,  4,  4,  4,  3, ...
224, 101,  35,  16,  12,   7,  4,  4,  4,  4,  4, ...
312, 135,  43,  21,  13,  10,  5,  4,  4,  4,  4, ...
432, 176,  55,  27,  14,  12,  7,  4,  4,  4,  4, ...
...

L. Euler, De mirabilibus proprietatibus numerorum pentagonalium
L. Euler, On the remarkable properties of the pentagonal numbers, arXiv:math/0505373 [math.HO], 2005.
Eric Weisstein's World of Mathematics, Pentagonal Number Theorem

Columns (0-10): A211971, A000041, A006950, A036820, A195848, A195849, A195850, A195851, A195852, A196933, A210964.
For another version see A195825.
Cf. A057077, A195152.

T(n,k) = A211971(n), if k = 0.

T(n,k) = A195825(n,k), if k >= 1.

A236002 Number of overcompositions of n.

Original entry on oeis.org

1, 2, 4, 12, 26, 60, 144, 324, 728, 1602, 3576, 7808, 17068, 36908, 79520, 170704, 364794, 777036, 1649456, 3491188, 7367544, 15513336, 32584648, 68307264, 142904080, 298448914, 622235060, 1295320004, 2692583916, 5589586996, 11588905844, 23999052692

Offset: 0

Omar E. Pol, Jan 19 2014

nonn

Analog to overpartitions, here an overcomposition is defined to be a composition in which the first occurrence of each distinct number may be overlined (see example).
Also 1 together with the row sums of A235999.
For the number of partitions of n see A000041.
For the number of compositions of n see A011782.
For the number of overpartitions of n see A015128.
Note that there are several orderings of overcompositions, the same as the orderings of compositions, but apparently for every ordering of overcompositions there are also several suborderings according to the arrangements of the overlined parts. The same for overpartitions. See one of them in Example section.

			For n = 4 the 26 overcompositions of 4 are: [4], [4'], [1,3], [1',3], [1,3'], [1',3'], [2,2], [2',2], [1,1,2], [1',1,2], [1,1,2'], [1',1,2'], [3,1], [3',1], [3,1'], [3',1'], [1,2,1], [1',2,1], [1,2',1], [1',2',1], [2,1,1], [2',1,1], [2,1',1], [2',1',1], [1,1,1,1], [1',1,1,1].

Alois P. Heinz, Table of n, a(n) for n = 0..1000

Cf. A000041, A011782, A015128, A235998, A235999, A238439.

a(n) = Sum_{k=1..A003056(n)} 2^k*A235998(n,k), n >= 1.

a(7) corrected and more terms added, Joerg Arndt, Jan 20 2014

a(19)-a(31) from Alois P. Heinz, Jan 20 2014

A160461 Coefficients in the expansion of C/B^2, in Watson's notation of page 106.

Original entry on oeis.org

1, 2, 5, 10, 20, 35, 63, 105, 175, 280, 444, 685, 1050, 1575, 2345, 3439, 5005, 7195, 10275, 14525, 20405, 28428, 39375, 54150, 74080, 100715, 136265, 183365, 245645, 327485, 434810, 574790, 756965, 992950, 1297940, 1690500, 2194642, 2839695, 3663225, 4711160

Offset: 0

N. J. A. Sloane, Nov 13 2009

			x^3+2*x^27+5*x^51+10*x^75+20*x^99+35*x^123+63*x^147+...

Seiichi Manyama, Table of n, a(n) for n = 0..1000
Watson, G. N., Ramanujans Vermutung ueber Zerfaellungsanzahlen. J. Reine Angew. Math. (Crelle), 179 (1938), 97-128.

Cf. Product_{n>=1} (1 - x^(5*n))^k/(1 - x^n)^(k + 1): this sequence (k=1), A160462 (k=2), A160463 (k=3), A160506 (k=4), A071734 (k=5), A160460 (k=6), A160521 (k=7), A278555 (k=12), A278556 (k=18), A278557 (k=24), A278558 (k=30).

Cf. A000041, A015128, A278690, A298311.

nmax = 50; CoefficientList[Series[Product[(1 - x^(5*k))/(1 - x^k)^2, {k, 1, nmax}], {x, 0, nmax}], x] (* Vaclav Kotesovec, Nov 26 2016 *)

See Maple code in A160458 for formula.
a(n) ~ sqrt(3)*exp(sqrt(6*n/5)*Pi)/(20*n). - Vaclav Kotesovec, Nov 26 2016
G.f.: 1/Product_{n > = 1} ( 1 - x^(n/gcd(n,k)) ) for k = 5. Cf. A000041 (k = 1), A015128 (k = 2), A278690 (k = 3) and A298311 (k = 4). - Peter Bala, Nov 17 2020

A235790 Triangle read by rows: T(n,k) = 2^k*A116608(n,k), n>=1, k>=1.

Original entry on oeis.org

2, 4, 4, 4, 6, 8, 4, 20, 8, 24, 8, 4, 44, 16, 8, 52, 40, 6, 68, 80, 8, 88, 120, 16, 4, 108, 200, 32, 12, 116, 296, 80, 4, 148, 416, 160, 8, 176, 536, 320, 8, 176, 776, 480, 32, 10, 220, 936, 832, 64, 4, 236, 1232, 1232, 160, 12, 272, 1472, 1872, 320

Offset: 1

Omar E. Pol, Jan 18 2014

It appears that T(n,k) is the number of overpartitions of n having k distinct parts. (This is true by definition, Joerg Arndt, Jan 20 2014).
Row n has length A003056(n) hence the first element of column k is in row A000217(k).
The first element of column k is A000079(k).

			Triangle begins:
2;
4;
4,    4;
6,    8;
4,   20;
8,   24,    8;
4,   44,   16;
8,   52,   40;
6,   68,   80;
8,   88,  120,   16;
4,  108,  200,   32;
12, 116,  296,   80;
4,  148,  416,  160;
8,  176,  536,  320;
8,  176,  776,  480,   32;
10, 220,  936,  832,   64;
4,  236, 1232, 1232,  160;
12, 272, 1472, 1872,  320;
4,  284, 1880, 2592,  640;
12, 324, 2216, 3632, 1152;
8,  328, 2704, 4944, 1856, 64;
...

Alois P. Heinz, Rows n = 1..500, flattened

Row sums give A015128, n >= 1.
Column 1 is A062011.
Cf. A000217, A003056, A116608, A196020, A211971, A235792, A235793, A235797, A235798, A235999, A236000, A236001.

b:= proc(n, i) option remember; `if`(n=0, 1, `if`(i<1, 0,
      expand(b(n, i-1)+add(x*b(n-i*j, i-1), j=1..n/i))))
    end:
T:= n->(p->seq(2^i*coeff(p, x, i), i=1..degree(p)))(b(n$2)):
seq(T(n), n=1..20);  # Alois P. Heinz, Jan 20 2014

b[n_, i_] := b[n, i] = If[n == 0, 1, If[i<1, 0, Expand[b[n, i-1] + Sum[x*b[n-i*j, i-1], {j, 1, n/i}]]]]; T[n_] := Function[p, Table[2^i * Coefficient[p, x, i], {i, 1, Exponent[p, x]}]][b[n, n]]; Table[T[n], {n, 1, 20}] // Flatten (* Jean-François Alcover, Oct 20 2016, after Alois P. Heinz *)

A261386 Expansion of Product_{k>=1} ((1+x^k)/(1-x^k))^(2*k).

Original entry on oeis.org

1, 4, 16, 56, 176, 520, 1456, 3896, 10048, 25100, 60960, 144440, 334752, 760456, 1696464, 3722224, 8043040, 17135624, 36031104, 74840568, 153680928, 312198160, 627828272, 1250540024, 2468443296, 4830809868, 9377190336, 18061370288, 34531009760, 65552873736

Offset: 0

Vaclav Kotesovec, Aug 17 2015

nonn

Convolution of A161870 and A026011.

Seiichi Manyama, Table of n, a(n) for n = 0..10000
Vaclav Kotesovec, A method of finding the asymptotics of q-series based on the convolution of generating functions, arXiv:1509.08708 [math.CO], Sep 30 2015, p. 19.

Cf. A015128, A026011, A156616, A161870, A216406, A261384, A261389.

nmax = 40; CoefficientList[Series[Product[(1+x^k)^(2*k) / (1-x^k)^(2*k), {k, 1, nmax}], {x, 0, nmax}], x]

a(n) ~ exp(1/6 + 3/2*(7*Zeta(3))^(1/3) * n^(2/3)) * (7*Zeta(3))^(2/9) / (A^2 * 2^(2/3) * n^(13/18) * sqrt(3*Pi)), where Zeta(3) = A002117 and A = A074962 is the Glaisher-Kinkelin constant.

G.f.: exp(Sum_{k>=1} (sigma_2(2*k) - sigma_2(k))*x^k/k). - Ilya Gutkovskiy, Apr 14 2019

A277212 Expansion of Product_{n>=1} (1 - x^(5*n))/(1 - x^n)^5 in powers of x.

Original entry on oeis.org

1, 5, 20, 65, 190, 505, 1260, 2970, 6700, 14535, 30520, 62235, 123720, 240340, 457380, 854190, 1568230, 2834120, 5048140, 8871450, 15396690, 26410860, 44811440, 75254240, 125162100, 206275505, 337032360, 546183425, 878270360, 1401857550, 2221862260

Offset: 0

Seiichi Manyama, Nov 07 2016

nonn

In general, for fixed m > 1, if g.f. = Product_{k>=1} (1 - x^(m*k))/(1 - x^k)^m, then a(n, m) ~ exp(Pi*sqrt(2*n*(m-1/m)/3)) * (m^2 - 1)^(m/4) / (2^(3*m/4 + 1/2) * 3^(m/4) * m^(m/4 + 1/2) * n^(m/4 + 1/2)). - Vaclav Kotesovec, Nov 10 2016

			G.f.: 1 + 5*x + 20*x^2 + 65*x^3 + 190*x^4 + 505*x^5 + 1260*x^6 + ...

Robert Israel, Table of n, a(n) for n = 0..10000
Eric Weisstein's World of Mathematics, q-Pochhammer Symbol

Cf. Expansion of Product_{n>=1} (1 - x^(k*n))/(1 - x^n)^k in powers of x: A015128 (k=2), A273845 (k=3), A274327 (k=4), this sequence (k=5), A160539 (k=7).

Cf. A109064.

N:= 100: # to get a(0)..a(N)
S:= series(mul((1-x^(5*n))/(1-x^n)^5,n=1..N),x,N+1):
seq(coeff(S,x,n),n=0..N); # Robert Israel, Nov 09 2016

nmax = 50; CoefficientList[Series[Product[(1 - x^(5*k))/(1 - x^k)^5, {k, 1, nmax}], {x, 0, nmax}], x] (* Vaclav Kotesovec, Nov 10 2016 *)
(QPochhammer[x^5, x^5]/QPochhammer[x, x]^5 + O[x]^40)[[3]] (* Vladimir Reshetnikov, Nov 20 2016 *)

first(n)=my(x='x); Vec(prod(k=1, n, (1-x^(5*k))/(1-x^k)^5, 1+O(x^(n+1)))) \\ Charles R Greathouse IV, Nov 07 2016

x='x+O('x^66); Vec(eta(x^5)/eta(x)^5) \\ Joerg Arndt, Nov 27 2016

G.f.: Product_{n>=1} (1 - x^(5*n))/(1 - x^n)^5.
a(n) ~ exp(4*Pi*sqrt(n/5)) / (sqrt(2) * 5^(7/4) * n^(7/4)). - Vaclav Kotesovec, Nov 10 2016
G.f.: (x^5; x^5)inf/((x; x)_inf)^5, where (a; q)_inf is the q-Pochhammer symbol. - _Vladimir Reshetnikov, Nov 20 2016
a(0) = 1, a(n) = (5/n)*Sum_{k=1..n} A285896(k)*a(n-k) for n > 0. - Seiichi Manyama, Apr 29 2017

A143184 Coefficients of a Ramanujan q-series.

Original entry on oeis.org

1, 1, 2, 4, 6, 10, 15, 23, 33, 49, 69, 98, 136, 188, 256, 348, 466, 622, 824, 1084, 1418, 1846, 2389, 3077, 3947, 5038, 6407, 8115, 10241, 12876, 16141, 20160, 25110, 31179, 38609, 47674, 58724, 72141, 88421, 108114, 131902, 160565, 195061, 236468

Offset: 0

Michael Somos, Jul 28 2008

nonn

Also equal to the number of overpartitions of n with no non-overlined parts larger than the number of overlined parts. For example, the overpartitions counted by a(4) = 6 are: [4'], [3',1], [3',1'], [2',1,1], [2',1',1], [1',1,1,1]. - Jeremy Lovejoy, Aug 23 2021

Also the number of partitions into red and blue integers, where the red parts cover an initial segment of the positive integers, and there can be no blue integer if there is not also a red one with the same value. For example, when the red integers are marked with a prime, the partitions counted by a(4) are: [2',1',1], [2',1',1'], [1',1,1,1], [1',1',1,1], [1',1',1',1], [1',1',1',1']. - Christian Sievers, May 09 2025

			G.f. = 1 + q + 2*q^2 + 4*q^3 + 6*q^4 + 10*q^5 + 15*q^6 + 23*q^7 + 33*q^8 + ...

S. Ramanujan, The Lost Notebook and Other Unpublished Papers, Narosa Publishing House, New Delhi, 1988, p. 10

Alois P. Heinz, Table of n, a(n) for n = 0..10000
G. E. Andrews, Ramanujan's "lost" notebook. IV. Stacks and alternating parity in partitions, Adv. in Math. 53 (1984), 55-74.
B. Kim, E. Kim, and J. Lovejoy, On weighted overpartitions related to some q-series in Ramanujan's lost notebook, Int. J. Number Theory 17 (2021), 603-619.

Convolution with A002448 is A132211.

Cf. A015128 (has definition of overpartitions).

b:= proc(n, i) option remember;
     `if`(i>n, 0, `if`(irem(n, i, 'r')=0, r, 0)+
      add(j*b(n-i*j, i+1), j=1..n/i))
    end:
a:= n-> `if`(n=0, 1, b(n, 1)):
seq(a(n), n=0..50);  # Alois P. Heinz, Oct 03 2018

m = 50;
Sum[x^(k(k+1)/2)/Product[1-x^j, {j, 1, k}]^2, {k, 0, m}] + O[x]^m // CoefficientList[#, x]& (* Jean-François Alcover, Nov 20 2020 *)

{a(n) = my(t); if(n<0, 0, t = 1 + x*O(x^n); polcoef(sum(k=1, (sqrtint(8*n + 1) - 1)\2, t = t*x^k/(1 - x^k)^2 + x*O(x^n), 1), n))};

G.f.: Sum_{k>=0} x^((k^2+k)/2) / ((1 - x) * (1 - x^2) ... (1 - x^k))^2.

a(n) ~ exp(2*Pi*sqrt(n/5)) / (2^(3/2) * 5^(3/4) * n). - Vaclav Kotesovec, Nov 20 2020

A261610 Expansion of Product_{k>=0} (1 + x^(3k+1))/(1 - x^(3k+1)).

Original entry on oeis.org

1, 2, 2, 2, 4, 6, 6, 8, 12, 14, 16, 22, 28, 32, 40, 50, 58, 70, 86, 100, 118, 144, 168, 194, 232, 272, 312, 366, 428, 490, 568, 660, 754, 866, 1000, 1140, 1300, 1492, 1696, 1924, 2196, 2490, 2812, 3192, 3610, 4062, 4588, 5174, 5806, 6530, 7342, 8218, 9208

Offset: 0

Vaclav Kotesovec, Aug 26 2015

nonn

Cf. A015128, A080054, A261611.

nmax = 60; CoefficientList[Series[Product[(1 + x^(3*k+1))/(1 - x^(3*k+1)), {k, 0, nmax}], {x, 0, nmax}], x]

a(n) ~ exp(Pi*sqrt(n/3)) * Gamma(1/3) / (2^(5/3) * 3^(1/3) * Pi^(2/3) * n^(2/3)).

A266648 Expansion of Product_{k>=1} (1 + x^(3*k)) / (1 - x^k).

Original entry on oeis.org

1, 1, 2, 4, 6, 9, 15, 21, 31, 46, 64, 89, 126, 170, 231, 314, 417, 552, 733, 955, 1244, 1617, 2079, 2665, 3413, 4331, 5485, 6931, 8704, 10901, 13629, 16949, 21033, 26045, 32123, 39529, 48553, 59429, 72599, 88518, 107624, 130599, 158209, 191175, 230611, 277717, 333730, 400375, 479598, 573386, 684481

Offset: 0

Vaclav Kotesovec, Jan 02 2016

nonn

a(n) is the number of overpartitions wherein only parts that are a multiple of three may be overlined. - Alois P. Heinz, Feb 03 2025

Vaclav Kotesovec, Table of n, a(n) for n = 0..5000
Wenjie Fang, Hsien-Kuei Hwang, and Mihyun Kang, Phase transitions from exp(n^(1/2)) to exp(n^(2/3)) in the asymptotics of banded plane partitions, arXiv:2004.08901 [math.CO], 2020, p. 6.
Vaclav Kotesovec, A method of finding the asymptotics of q-series based on the convolution of generating functions, arXiv:1509.08708 [math.CO], 2015-2016.

Cf. A000726, A015128, A100405, A266647, A266649, A266650, A285445, A285447.

b:= proc(n, i) option remember; `if`(n=0, 1, `if`(i<1, 0,
      b(n, i-1)+`if`(irem(i, 3)=0, 2, 1)*add(b(n-i*j, i-1), j=1..n/i)))
    end:
a:= n-> b(n$2):
seq(a(n), n=0..50);  # Alois P. Heinz, Feb 03 2025

nmax = 50; CoefficientList[Series[Product[(1+x^(3*k))/(1-x^k), {k, 1, nmax}], {x, 0, nmax}], x]

a(n) ~ sqrt(7) * exp(sqrt(7*n)*Pi/3) / (24*n).

A338223 G.f.: (1 / theta_4(x) - 1)^2 / 4, where theta_4() is the Jacobi theta function.

Original entry on oeis.org

1, 4, 12, 30, 68, 144, 289, 556, 1034, 1868, 3292, 5678, 9608, 15984, 26188, 42314, 67509, 106460, 166090, 256552, 392628, 595696, 896484, 1338894, 1985298, 2923840, 4278448, 6222518, 8997544, 12938368, 18507297, 26340040, 37307326, 52597320, 73825504, 103180702

Offset: 2

Ilya Gutkovskiy, Jan 30 2021

nonn

Alois P. Heinz, Table of n, a(n) for n = 2..10000

Cf. A001934, A002448, A014968, A015128, A048574, A063725, A327380.

g:= proc(n, i) option remember; `if`(n=0, 1/2, `if`(i=1, 0,
      g(n, i-1))+add(2*g(n-i*j, i-1), j=`if`(i=1, n, 1)..n/i))
    end:
b:= proc(n, k) option remember; `if`(k=0, 1, `if`(k=1, `if`(n=0, 0,
      g(n$2)), (q-> add(b(j, q)*b(n-j, k-q), j=0..n))(iquo(k, 2))))
    end:
a:= n-> b(n, 2):
seq(a(n), n=2..37);  # Alois P. Heinz, Feb 10 2021

nmax = 37; CoefficientList[Series[(1/EllipticTheta[4, 0, x] - 1)^2/4, {x, 0, nmax}], x] // Drop[#, 2] &
nmax = 37; CoefficientList[Series[(1/4) (-1 + Product[(1 + x^k)/(1 - x^k), {k, 1, nmax}])^2, {x, 0, nmax}], x] // Drop[#, 2] &
A015128[n_] := Sum[PartitionsP[k] PartitionsQ[n - k], {k, 0, n}]; a[n_] := (1/4) Sum[A015128[k] A015128[n - k], {k, 1, n - 1}]; Table[a[n], {n, 2, 37}]

G.f.: (1/4) * (-1 + Product_{k>=1} (1 + x^k) / (1 - x^k))^2.
a(n) = Sum_{k=0..n} A014968(k) * A014968(n-k).
a(n) = (1/4) * Sum_{k=1..n-1} A015128(k) * A015128(n-k).
a(n) = (A001934(n) - 2 * A015128(n)) / 4 for n > 0.

cp's OEIS Frontend

A211970 Square array read by antidiagonal: T(n,k), n >= 0, k >= 0, which arises from a generalization of Euler's Pentagonal Number Theorem.

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A236002 Number of overcompositions of n.

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A160461 Coefficients in the expansion of C/B^2, in Watson's notation of page 106.

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A235790 Triangle read by rows: T(n,k) = 2^k*A116608(n,k), n>=1, k>=1.

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Mathematica

A261386 Expansion of Product_{k>=1} ((1+x^k)/(1-x^k))^(2*k).

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A277212 Expansion of Product_{n>=1} (1 - x^(5*n))/(1 - x^n)^5 in powers of x.

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Maple

Mathematica

PARI

PARI

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A143184 Coefficients of a Ramanujan q-series.

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Maple

Mathematica

PARI

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A261610 Expansion of Product_{k>=0} (1 + x^(3*k+1))/(1 - x^(3*k+1)).

A261610 Expansion of Product_{k>=0} (1 + x^(3k+1))/(1 - x^(3k+1)).