OFFSET
1,1
FORMULA
G.f.: Sum_{k>0} binomial(k+2,2) * x^k/(1 - x^k).
a(n) = Sum_{d|n} binomial(d+2,2).
MATHEMATICA
a[n_] := DivisorSum[n, Binomial[# + 2, 2] &]; Array[a, 50] (* Amiram Eldar, Jul 05 2023 *)
PROG
(PARI) a(n) = sumdiv(n, d, binomial(d+2, 2));
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Jun 12 2023
STATUS
approved