OFFSET
1,6
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^2/28 = 0.352485... . - Amiram Eldar, Apr 12 2024
MATHEMATICA
Table[Sum[If[Mod[d, 7] <2 || Mod[d, 7]==6, d, 0], {d, Divisors[n]}], {n, 80}] (* Indranil Ghosh, Mar 25 2017 *)
PROG
(PARI) a(n) = sumdiv(n, d, ((d + 1) % 7 < 3) * d); \\ Amiram Eldar, Apr 12 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Mar 25 2017
STATUS
approved