OFFSET
1,2
LINKS
Winston de Greef, Table of n, a(n) for n = 1..385
FORMULA
G.f.: Sum_{k>=1} ( (k + x^k)^k - k^k ).
If p is prime, a(p) = p^p.
MATHEMATICA
a[n_] := DivisorSum[n, #^(# - n/#) * Binomial[#, n/#] &]; Array[a, 20] (* Amiram Eldar, Apr 24 2021 *)
PROG
(PARI) a(n) = sumdiv(n, d, d^(d-n/d)* binomial(d, n/d));
(PARI) N=20; x='x+O('x^N); Vec(sum(k=1, N, (k+x^k)^k-k^k))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Apr 24 2021
STATUS
approved