OFFSET
0,2
FORMULA
a(n) ~ c * (-2)^n, where c = QPochhammer[-1, -1/2]/QPochhammer[-1/2] = 0.93943604828296530723602398257349307281... - Vaclav Kotesovec, Apr 25 2018
MATHEMATICA
nmax = 40; CoefficientList[Series[Product[(1 - 2*x^k)/(1 + 2*x^k), {k, 1, nmax}], {x, 0, nmax}], x] (* Vaclav Kotesovec, Apr 25 2018 *)
PROG
(PARI) N=66; x='x+O('x^N); Vec(prod(k=1, N, (1-2*x^k)/(1+2*x^k)))
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Apr 23 2018
STATUS
approved