OFFSET
0,3
LINKS
Vaclav Kotesovec, Table of n, a(n) for n = 0..610
FORMULA
E.g.f.: Product_{k>=1} (1 + x^k / k!)^sigma_0(k).
MATHEMATICA
nmax = 24; CoefficientList[Series[Product[(1 + x^k/k!)^DivisorSigma[0, k], {k, 1, nmax}], {x, 0, nmax}], x] Range[0, nmax]!
a[n_] := a[n] = If[n == 0, 1, -(n - 1)! Sum[Sum[d DivisorSigma[0, d]/(-d!)^(k/d), {d, Divisors[k]}] a[n - k]/(n - k)!, {k, 1, n}]]; Table[a[n], {n, 0, 24}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Feb 13 2021
STATUS
approved