OFFSET
1,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..152
FORMULA
L.g.f.: -log(Product_{k>=1} (1 - x^k)^(k^(3*k-1))) = Sum_{k>=1} a(k)*x^k/k.
G.f.: Sum_{k>=1} k^(3*k) * x^k/(1 - x^k).
MATHEMATICA
a[n_] := DivisorSum[n, #^(3*#) &]; Array[a, 12] (* Amiram Eldar, May 09 2021 *)
PROG
(PARI) {a(n) = sumdiv(n, d, d^(3*d))}
(PARI) N=20; x='x+O('x^N); Vec(x*deriv(-log(prod(k=1, N, (1-x^k)^k^(3*k-1)))))
(PARI) N=20; x='x+O('x^N); Vec(sum(k=1, N, k^(3*k)*x^k/(1-x^k)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jun 17 2019
STATUS
approved