OFFSET
1,4
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..10000
FORMULA
Sum_{k=1..n} a(k) ~ c * n^2, where c = Pi^2/20 = A102753 / 10 = 0.4934802... . - Amiram Eldar, Apr 12 2024
MATHEMATICA
Table[Sum[If[Mod[d, 5]<2 || Mod[d, 5]==4, d, 0], {d, Divisors[n]}], {n, 80}] (* Indranil Ghosh, Mar 25 2017 *)
Table[Total[Select[Divisors[n], MemberQ[{0, 1, 4}, Mod[#, 5]]&]], {n, 70}] (* Harvey P. Dale, Aug 02 2020 *)
PROG
(PARI) a(n) = sumdiv(n, d, ((d + 1) % 5 < 3) * d); \\ Amiram Eldar, Apr 12 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Mar 25 2017
STATUS
approved