OFFSET
0,3
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..80
FORMULA
a(n) = [x^n] Product_{i>=1, j>=1} 1/(1 - x^(i*j))^(j^n).
a(n) = [x^n] exp(Sum_{k>=1} sigma_(n+1)(k)*x^k/(k*(1 - x^k))).
MAPLE
with(numtheory):
b:= proc(n, k) option remember; `if`(n=0, 1, add(add(d*
sigma[k](d), d=divisors(j))*b(n-j, k), j=1..n)/n)
end:
a:= n-> b(n$2):
seq(a(n), n=0..20); # Alois P. Heinz, Oct 26 2018
MATHEMATICA
Table[SeriesCoefficient[Product[1/(1 - x^k)^DivisorSigma[n, k], {k, 1, n}], {x, 0, n}], {n, 0, 16}]
Table[SeriesCoefficient[Product[Product[1/(1 - x^(i j))^(j^n), {j, 1, n}], {i, 1, n}], {x, 0, n}], {n, 0, 16}]
Table[SeriesCoefficient[Exp[Sum[DivisorSigma[n + 1, k] x^k/(k (1 - x^k)), {k, 1, n}]], {x, 0, n}], {n, 0, 16}]
PROG
(PARI) {a(n) = polcoeff(prod(k=1, n, 1/(1-x^k+x*O(x^n))^sigma(k, n)), n)} \\ Seiichi Manyama, Oct 27 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Oct 26 2018
STATUS
approved