A035295 Expansion of sum ( q^n / product( 1-q^k, k=1..3*n), n=0..inf ).

1, 1, 2, 4, 7, 11, 17, 26, 38, 54, 77, 107, 148, 201, 272, 363, 483, 635, 832, 1081, 1399, 1796, 2299, 2924, 3707, 4673, 5874, 7348, 9166, 11384, 14102, 17404, 21425, 26285, 32172, 39259, 47799, 58036, 70318, 84985, 102507, 123354, 148163, 177582, 212464, 253692, 302411

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn

Links

• Vaclav Kotesovec, Table of n, a(n) for n = 0..5000

Crossrefs

Cf. A363066, A385067.

Programs

Mathematica

nmax = 50; CoefficientList[Series[Sum[x^k/Product[1 - x^j, {j, 1, 3*k}], {k, 0, nmax}], {x, 0, nmax}], x]  (* Vaclav Kotesovec, Jun 16 2025 *)
nmax = 50; p=1; s=1; Do[p=Expand[p*(1-x^(3*k))*(1-x^(3*k-1))*(1-x^(3*k-2))];p=Take[p, Min[nmax+1, Exponent[p, x]+1, Length[p]]];s+=x^k/p;, {k, 1, nmax}]; CoefficientList[Series[s, {x, 0, nmax}], x] (* Vaclav Kotesovec, Jun 16 2025 *)

Formula

a(n) ~ Gamma(1/3) * exp(Pi*sqrt(2*n/3)) / (2^(5/3) * 3^(7/6) * Pi^(2/3) * n^(2/3)). - Vaclav Kotesovec, Jun 16 2025

Extensions

More terms from Vaclav Kotesovec, Jun 16 2025