OFFSET
0,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
T. Ishikawa, Congruences between binomial coefficients binom(2f,f) and Fourier coefficients of certain eta-products, Hiroshima Math. J. 22 (1992), no. 3, 583-590.
FORMULA
Euler transform of period 8 sequence [ -2, -6, -2, 0, -2, -6, -2, -4, ...]. - Michael Somos, Mar 01 2008
EXAMPLE
q^3 - 2*q^7 - 5*q^11 + 10*q^15 + 13*q^19 - 22*q^23 - 30*q^27 + ...
MATHEMATICA
QP = QPochhammer; s = QP[q]^2*QP[q^2]^4*(QP[q^8]^4/QP[q^4]^6) + O[q]^50; CoefficientList[s, q] (* Jean-François Alcover, Nov 27 2015, adapted from PARI *)
PROG
(PARI) {a(n) = local(A); if( n<0, 0, A = x * O(x^n); polcoeff( (eta(x + A) * eta(x^2 + A)^2 / eta(x^4 + A)^3 * eta(x^8 + A)^2)^2, n))} /* Michael Somos, Mar 01 2008 */
CROSSREFS
KEYWORD
sign
AUTHOR
N. J. A. Sloane, Feb 07 2008
STATUS
approved