OFFSET
1,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..10000
FORMULA
G.f.: (1/2) * Sum_{k >= 1} ((1 + x^k)^k - (1 - x^k)^k).
If p is prime, a(p) = p.
MATHEMATICA
a[n_] := DivisorSum[n, Binomial[n/#, #] &, OddQ[#] &]; Array[a, 75] (* Amiram Eldar, Apr 25 2021 *)
PROG
(PARI) a(n) = sumdiv(n, d, (d%2)*binomial(n/d, d));
(PARI) N=99; x='x+O('x^N); Vec(sum(k=1, N, (1+x^k)^k-(1-x^k)^k)/2)
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Apr 25 2021
STATUS
approved