OFFSET
1,5
FORMULA
a(n) = (1/5) * Sum_{d | 5*n-4, d==2 (mod 5)} (d+3).
G.f.: Sum_{k>0} x^(2*k) / (1 - x^(5*k-2))^2.
MATHEMATICA
a[n_] := DivisorSum[5*n - 4, # + 3 &, Mod[#, 5] == 2 &]/5; Array[a, 100] (* Amiram Eldar, Jul 06 2023 *)
PROG
(PARI) a(n) = sumdiv(5*n-4, d, (d%5==2)*(d+3))/5;
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jul 06 2023
STATUS
approved