OFFSET
1,2
FORMULA
E.g.f.: -(1/(1-x)) * Sum_{k>0} log(1 - (k*x)^k)/k.
a(n) ~ n! * n^(n-1). - Vaclav Kotesovec, Aug 07 2022
MATHEMATICA
Table[n! * Sum[DivisorSigma[k, k]/k, {k, 1, n}], {n, 1, 20}] (* Vaclav Kotesovec, Aug 07 2022 *)
PROG
(PARI) a(n) = n!*sum(k=1, n, sigma(k, k)/k);
(PARI) my(N=20, x='x+O('x^N)); Vec(serlaplace(-sum(k=1, N, log(1-(k*x)^k)/k)/(1-x)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Aug 07 2022
STATUS
approved