OFFSET
1,3
FORMULA
E.g.f.: Sum_{k>0} (1 - exp(-x^k))/k!.
If p is an odd prime, a(p) = 2.
MATHEMATICA
a[n_] := n! * DivisorSum[n, (-1)^(#+1)/(#! * (n/#)!) &]; Array[a, 30] (* Amiram Eldar, Jul 03 2023 *)
PROG
(PARI) a(n) = n!*sumdiv(n, d, (-1)^(d+1)/(d!*(n/d)!));
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Jun 18 2023
STATUS
approved