OFFSET
1,2
LINKS
Michael De Vlieger, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = Sum_{k=1..n} binomial(k+1,2) * (floor(n/k) mod 2).
G.f.: -1/(1-x) * Sum_{k>=1} (-x)^k/(1-x^k)^3 = 1/(1-x) * Sum_{k>=1} binomial(k+1,2) * x^k/(1+x^k).
MATHEMATICA
Array[Sum[(-1)^(k - 1)*Binomial[Floor[#/k] + 2, 3], {k, #}] &, 56] (* Michael De Vlieger, Oct 25 2023 *)
PROG
(PARI) a(n) = sum(k=1, n, (-1)^(k-1)*binomial(n\k+2, 3));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Oct 24 2023
STATUS
approved