OFFSET
1,2
LINKS
Winston de Greef, Table of n, a(n) for n = 1..10000
FORMULA
MATHEMATICA
a[n_] := Sum[(-1)^(k + 1) * Floor[n/(2*k - 1)]^2, {k, 1, n}]; Array[a, 50] (* Amiram Eldar, Dec 18 2021 *)
PROG
(PARI) a(n) = sum(k=1, n, (-1)^(k+1)*(n\(2*k-1))^2);
(PARI) a(n) = sum(k=1, n, sumdiv(k, d, kronecker(-4, k/d)*(2*d-1)));
(PARI) my(N=66, x='x+O('x^N)); Vec(sum(k=1, N, (2*k-1)*x^k/(1+x^(2*k)))/(1-x))
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Dec 18 2021
STATUS
approved