OFFSET
1,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..605
FORMULA
G.f.: Sum_{k>0} x^k / (1 - (k * x)^k / k).
If p is prime, a(p) = 2.
MATHEMATICA
a[n_] := DivisorSum[n, #^(n + 1 - # - n/#) &]; Array[a, 32] (* Amiram Eldar, Aug 09 2023 *)
PROG
(PARI) a(n) = sumdiv(n, d, d^(n+1-d-n/d));
(PARI) my(N=40, x='x+O('x^N)); Vec(sum(k=1, N, x^k/(1-(k*x)^k/k)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jan 14 2023
STATUS
approved