OFFSET
1,2
LINKS
Winston de Greef, Table of n, a(n) for n = 1..384
FORMULA
G.f.: Sum_{k >= 1} ((1 + (k * x)^k)^k - 1).
If p is prime, a(p) = p^(p+1).
MATHEMATICA
a[n_] := DivisorSum[n, #^n * Binomial[#, n/#] &]; Array[a, 20] (* Amiram Eldar, Apr 24 2021 *)
PROG
(PARI) a(n) = sumdiv(n, d, d^n*binomial(d, n/d));
(PARI) N=20; x='x+O('x^N); Vec(sum(k=1, N, (1+(k*x)^k)^k-1))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Apr 23 2021
STATUS
approved