OFFSET
1,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..10000
FORMULA
G.f.: Sum_{k>=0} (k^2+1) * x^(k^2+1)/(1 - x^(k^2+1)).
Sum_{k=1..n} a(k) ~ zeta(3/2)*n^(3/2)/3. - Vaclav Kotesovec, Jan 21 2023
MATHEMATICA
Table[Sum[If[IntegerQ[Sqrt[d-1]], d, 0], {d, Divisors[n]}], {n, 1, 100}] (* Vaclav Kotesovec, Jan 21 2023 *)
PROG
(PARI) a(n) = sumdiv(n, d, issquare(d-1)*d);
(PARI) my(N=100, x='x+O('x^N)); Vec(sum(k=0, sqrtint(N), (k^2+1)*x^(k^2+1)/(1-x^(k^2+1))))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jan 19 2023
STATUS
approved