OFFSET
1,5
FORMULA
a(n) = Sum_{d|n, d==2 mod 3} ((d+1)/3)^2.
MATHEMATICA
a[n_] := DivisorSum[n, ((#+1)/3)^2 &, Mod[#, 3] == 2 &]; Array[a, 100] (* Amiram Eldar, Jun 30 2023 *)
PROG
(PARI) a(n) = sumdiv(n, d, (d%3==2)*((d+1)/3)^2);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Jun 30 2023
STATUS
approved