OFFSET
1,2
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = A284280(5*n-4).
G.f.: Sum_{k>0} (5*k-3) * x^(3*k-1) / (1 - x^(5*k-3)).
MAPLE
f:= n ->
convert(select(t -> t mod 5 = 2, numtheory:-divisors(5*n-4)), `+`):
map(f, [$1..100]); # Robert Israel, Jul 23 2023
MATHEMATICA
a[n_] := DivisorSum[5*n - 4, # &, Mod[#, 5] == 2 &]; Array[a, 100] (* Amiram Eldar, Jul 06 2023 *)
PROG
(PARI) a(n) = sumdiv(5*n-4, d, (d%5==2)*d);
CROSSREFS
KEYWORD
nonn,look
AUTHOR
Seiichi Manyama, Jul 06 2023
STATUS
approved