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A303397 Expansion of Product_{k>=1} (1 - 2*x^k)/(1 + 2*x^k). 2
1, -4, 4, -4, 20, -36, 52, -116, 244, -500, 964, -1876, 3876, -7780, 15332, -30628, 61684, -123460, 246036, -491988, 985492, -1971284, 3939556, -7878068, 15762692, -31527428, 63041220, -126078916, 252185044, -504375460, 1008698036, -2017385268, 4034873268 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..32.

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

Expansion of Product_{k>=1} (1 - b*x^k)/(1 + b*x^k): A002448 (b=1), this sequence (b=2), A303398 (b=3).

Cf. A261584, A303345.

Sequence in context: A320970 A216871 A120914 * A024949 A059812 A077725

Adjacent sequences:  A303394 A303395 A303396 * A303398 A303399 A303400

KEYWORD

sign

AUTHOR

Seiichi Manyama, Apr 23 2018

STATUS

approved

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Last modified June 5 11:06 EDT 2020. Contains 334840 sequences. (Running on oeis4.)