OFFSET
1,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..1000
FORMULA
G.f.: Sum_{k>0} x^k / (1 - 2 * k * x^k).
If p is prime, a(p) = 1 + 2^(p-1).
MATHEMATICA
a[n_] := DivisorSum[n, (2*#)^(n/# - 1) &]; Array[a, 30] (* Amiram Eldar, Aug 14 2023 *)
PROG
(PARI) a(n) = sumdiv(n, d, (2*d)^(n/d-1));
(PARI) my(N=40, x='x+O('x^N)); Vec(sum(k=1, N, x^k/(1-2*k*x^k)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jan 13 2023
STATUS
approved