OFFSET
1,2
COMMENTS
Not multiplicative: a(3)*a(7) <> a(21), for example. - R. J. Mathar, Dec 20 2011
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
FORMULA
From Amiram Eldar, Nov 05 2023: (Start)
Sum_{k=1..n} a(k) ~ c * n^3 / 3, where c = Pi^3/64 + 7*zeta(3)/16 = 1.010372968262... . (End)
MAPLE
A050461 := proc(n)
a := 0 ;
for d in numtheory[divisors](n) do
if (n/d) mod 4 = 1 then
a := a+d^2 ;
end if;
end do:
a;
end proc:
seq(A050461(n), n=1..40) ; # R. J. Mathar, Dec 20 2011
MATHEMATICA
a[n_] := DivisorSum[n, Boole[Mod[n/#, 4] == 1]*#^2&]; Array[a, 50] (* Jean-François Alcover, Feb 12 2018 *)
PROG
(Haskell)
a050461 n = sum [d ^ 2 | d <- a027750_row n, mod (div n d) 4 == 1]
-- Reinhard Zumkeller, Mar 06 2012
(PARI) a(n) = sumdiv(n, d, (n/d % 4 == 1) * d^2); \\ Amiram Eldar, Nov 05 2023
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Dec 23 1999
STATUS
approved