OFFSET
1,2
FORMULA
a(n) = Sum_{d|n} d^(d+n/d-1) * binomial(d+n/d-1,d).
If p is prime, a(p) = p + p^p.
MATHEMATICA
a[n_] := DivisorSum[n, #^(# + n/# - 1) * Binomial[# + n/# - 1, #] &]; Array[a, 20] (* Amiram Eldar, Jul 31 2023 *)
PROG
(PARI) my(N=20, x='x+O('x^N)); Vec(sum(k=1, N, (k*x)^k/(1-k*x^k)^(k+1)))
(PARI) a(n) = sumdiv(n, d, d^(d+n/d-1)*binomial(d+n/d-1, d));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Feb 22 2023
STATUS
approved