OFFSET
1,8
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = Sum_{d|n, n/d==4 mod 5} d.
G.f.: Sum_{k>0} x^(5*k-1) / (1 - x^(5*k-1))^2.
MATHEMATICA
a[n_] := DivisorSum[n, # &, Mod[n/#, 5] == 4 &]; Array[a, 100] (* Amiram Eldar, Jun 27 2023 *)
PROG
(PARI) a(n) = sumdiv(n, d, (n/d%5==4)*d);
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jun 27 2023
STATUS
approved