OFFSET
1,2
FORMULA
G.f.: Sum_{k>0} (k-1)! * (x/(1 - x^k))^k.
If p is prime, a(p) = 1 + (p-1)!.
MATHEMATICA
a[n_] := DivisorSum[n, (# + n/# - 2)!/(# - 1)! &]; Array[a, 23] (* Amiram Eldar, Aug 30 2023 *)
PROG
(PARI) a(n) = sumdiv(n, d, (d+n/d-2)!/(d-1)!);
(PARI) my(N=30, x='x+O('x^N)); Vec(sum(k=1, N, (k-1)!*(x/(1-x^k))^k))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Nov 14 2022
STATUS
approved