OFFSET
1,3
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = A078181(3*n-1).
G.f.: Sum_{k>0} (3*k-2) * x^(2*k-1)/(1 - x^(3*k-2)).
MATHEMATICA
a[n_] := DivisorSum[3*n - 1, # &, Mod[#, 3] == 1 &]; Array[a, 100] (* Amiram Eldar, Jun 26 2023 *)
PROG
(PARI) a(n) = sumdiv(3*n-1, d, (d%3==1)*d);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jun 26 2023
STATUS
approved