OFFSET
1,5
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..10000
FORMULA
G.f.: Sum_{k>=1} (6*k - 1)*x^(6*k-1)/(1 - x^(6*k-1)). - Ilya Gutkovskiy, Mar 21 2017
Sum_{k=1..n} a(k) = c * n^2 + O(n*log(n)), where c = Pi^2/72 = 0.137077... (A086729). - Amiram Eldar, Nov 26 2023
MATHEMATICA
Table[Sum[If[Mod[d, 6] == 5, d, 0], {d, Divisors[n]}], {n, 80}] (* Indranil Ghosh, Mar 21 2017 *)
Table[Total[Select[Divisors[n], Mod[#, 6]==5&]], {n, 80}] (* Harvey P. Dale, Dec 30 2017 *)
PROG
(PARI) for(n=1, 80, print1(sumdiv(n, d, if(Mod(d, 6)==5, d, 0)), ", ")) \\ Indranil Ghosh, Mar 21 2017
(Python)
from sympy import divisors
def a(n): return sum([d for d in divisors(n) if d%6==5]) # Indranil Ghosh, Mar 21 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Seiichi Manyama, Mar 20 2017
STATUS
approved