OFFSET
1,6
LINKS
FORMULA
a(n) = Sum_{d|n, d<n} [3 == d mod 4]*d.
G.f.: Sum_{k>=1} (4*k-1) * x^(8*k-2) / (1 - x^(4*k-1)). - Ilya Gutkovskiy, Apr 14 2021
Sum_{k=1..n} a(k) = c * n^2 + O(n*log(n)), where c = Pi^2/48 - 1/8 = 0.0806167... . - Amiram Eldar, Nov 27 2023
MATHEMATICA
Array[DivisorSum[#, # &, Mod[#, 4] == 3 &] - Boole[Mod[#, 4] == 3] # &, 105] (* Michael De Vlieger, Oct 23 2017 *)
PROG
(PARI) A293903(n) = sumdiv(n, d, (d<n)*(3==(d%4))*d);
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Antti Karttunen, Oct 19 2017
STATUS
approved