OFFSET
1,3
LINKS
Seiichi Manyama, Table of n, a(n) for n = 1..3000
FORMULA
G.f.: (1/(1 + 2*x)) * Sum_{k>=1} (-2)^(k-1)*x^k * (1 - (-2*x)^k)/(1 - (-2)^(k-1)*x^k).
MATHEMATICA
a[n_] := Sum[(-2)^(n - Floor[n/k]), {k, 1, n}]; Array[a, 30] (* Amiram Eldar, Jun 08 2021 *)
PROG
(PARI) a(n) = sum(k=1, n, (-2)^(n-n\k));
(PARI) my(N=40, x='x+O('x^N)); Vec(sum(k=1, N, (-2)^(k-1)*x^k*(1-(-2*x)^k)/(1-(-2)^(k-1)*x^k))/(1+2*x))
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Jun 08 2021
STATUS
approved