OFFSET
1,2
FORMULA
G.f.: Sum_{k >= 1} (x/(1 - (k * x)^k))^k.
If p is prime, a(p) = 2.
MATHEMATICA
a[n_] := DivisorSum[n, #^(n - #) * Binomial[# + n/# - 2, # - 1] &]; Array[a, 30] (* Amiram Eldar, Apr 25 2021 *)
PROG
(PARI) a(n) = sumdiv(n, d, d^(n-d)*binomial(d+n/d-2, d-1));
(PARI) my(N=40, x='x+O('x^N)); Vec(sum(k=1, N, (x/(1-(k*x)^k))^k))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Apr 24 2021
STATUS
approved