OFFSET
1,2
FORMULA
E.g.f.: (1/(1-x)) * Sum_{k>0} (exp(x^k) - 1)/k!.
a(n) = n! * Sum_{k=1..n} A121860(k)/k!.
MATHEMATICA
a[n_] := n! * Sum[DivisorSum[k, 1/(#!*(k/#)!) &], {k, 1, n}]; Array[a, 21] (* Amiram Eldar, Jul 22 2022 *)
PROG
(PARI) a(n) = n!*sum(k=1, n, sumdiv(k, d, 1/(d!*(k/d)!)));
(PARI) my(N=30, x='x+O('x^N)); Vec(serlaplace(sum(k=1, N, (exp(x^k)-1)/k!)/(1-x)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jul 22 2022
STATUS
approved