OFFSET
1,5
LINKS
Vaclav Kotesovec, Table of n, a(n) for n = 1..20000
FORMULA
G.f.: Sum_{k>=1} x^(3*k^2)/Product_{j=1..3*k-1} (1-x^j).
MATHEMATICA
CoefficientList[Series[Sum[x^(3k^2)/Product[1-x^j, {j, 3k-1}], {k, 64}], {x, 0, 64}], x] (* Stefano Spezia, Jan 22 2022 *)
Table[Count[IntegerPartitions[n], _?(3#[[-1]]==Length[#]&)], {n, 70}] (* Harvey P. Dale, Jul 13 2023 *)
PROG
(PARI) my(N=66, x='x+O('x^N)); concat([0, 0], Vec(sum(k=1, sqrtint(N\3), x^(3*k^2)/prod(j=1, 3*k-1, 1-x^j))))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jan 21 2022
STATUS
approved