OFFSET
0,6
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..10000 (first 501 terms from Seiichi Manyama)
MAPLE
b:= proc(n, i) option remember; `if`(n=0, 1, `if`(i<1, 0,
add(b(n-i*j, i-1)*j!*(-1)^j, j=0..min(2, n/i))))
end:
a:= n-> b(n$2):
seq(a(n), n=0..60); # Alois P. Heinz, Oct 04 2017
MATHEMATICA
nmax = 100; CoefficientList[Series[Product[1 - x^k + 2*x^(2*k), {k, 1, nmax}], {x, 0, nmax}], x] (* Vaclav Kotesovec, Oct 05 2017 *)
PROG
(PARI) Vec(prod(m=1, 80, 1-x^m+2*x^(2*m)) + O(x^80)) \\ Michel Marcus, Oct 04 2017
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Oct 03 2017
STATUS
approved