OFFSET
0,2
FORMULA
a(n) ~ c * (-4)^n, where c = QPochhammer[-1, -1/4]/QPochhammer[-1/4] = 1.3264181585010678966173808329272239860188791629... - Vaclav Kotesovec, Apr 25 2018
MATHEMATICA
nmax = 30; CoefficientList[Series[Product[(1 - 4*x^k)/(1 + 4*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, (1-4*x^k)/(1+4*x^k)))
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, Apr 23 2018
STATUS
approved