OFFSET
1,2
LINKS
Winston de Greef, Table of n, a(n) for n = 1..383
FORMULA
G.f.: Sum_{k>0} k^k * ( (1 + k*x^k)^k - 1 ).
If p is prime, a(p) = p^(p+2).
MATHEMATICA
a[n_] := DivisorSum[n, #^(# + n/#) * Binomial[#, n/#] &]; Array[a, 20] (* Amiram Eldar, Aug 02 2023 *)
PROG
(PARI) a(n) = sumdiv(n, d, d^(d+n/d)*binomial(d, n/d));
(PARI) my(N=20, x='x+O('x^N)); Vec(sum(k=1, N, k^k*((1+k*x^k)^k-1)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Feb 19 2023
STATUS
approved