OFFSET
1,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..386
FORMULA
G.f.: Sum_{k>0} (k * x)^k / (1 - k * x^k).
If p is prime, a(p) = 1 + p^p.
MATHEMATICA
a[n_] := DivisorSum[n, #^(# + n/# - 1) &]; Array[a, 20] (* Amiram Eldar, Aug 14 2023 *)
PROG
(PARI) a(n) = sumdiv(n, d, d^(d+n/d-1));
(PARI) my(N=20, x='x+O('x^N)); Vec(sum(k=1, N, (k*x)^k/(1-k*x^k)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jan 11 2023
STATUS
approved