OFFSET
1,3
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..10000 (first 1000 terms from Harvey P. Dale)
Mariusz SkaĆba, A Note on Sums of Two Squares and Sum-of-divisors Functions, INTEGERS 20A (2020) A92.
FORMULA
G.f.: Sum_{k>=1} (4*k - 1)*x^(4*k-1)/(1 - x^(4*k-1)). - Ilya Gutkovskiy, Mar 21 2017
Sum_{k=1..n} a(k) = c * n^2 + O(n*log(n)), where c = Pi^2/48 = 0.205616... (A245058). - Amiram Eldar, Nov 26 2023
MAPLE
A050452 := proc(n)
a := 0 ;
for d in numtheory[divisors](n) do
if d mod 4 = 3 then
a := a+d ;
end if;
end do:
a;
end proc:
seq(A050452(n), n=1..40) ; # R. J. Mathar, Dec 20 2011
MATHEMATICA
Table[Total[Select[Divisors[n], Mod[#, 4]==3&]], {n, 80}] (* Harvey P. Dale, Jul 07 2013 *)
PROG
(PARI) a(n) = sumdiv(n, d, d*((d % 4) == 3)); \\ Amiram Eldar, Nov 26 2023
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Dec 23 1999
STATUS
approved