OFFSET
1,2
FORMULA
a(n) = (n-1)! * A055225(n).
E.g.f.: -Sum_{k>0} log(1 - k * x^k)/k.
If p is prime, a(p) = (p-1)! + p!.
MATHEMATICA
a[n_] := (n - 1)! * DivisorSum[n, #^(n/#) &]; Array[a, 20] (* Amiram Eldar, Jun 08 2022 *)
PROG
(PARI) a(n) = (n-1)!*sumdiv(n, d, d^(n/d));
(PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(-sum(k=1, N, log(1-k*x^k)/k)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jun 08 2022
STATUS
approved