OFFSET
1,2
LINKS
FORMULA
Expansion of eta(q)^2 * eta(q^3)^2 * eta(q^6)^3 / eta(q^2) in powers of q.
Euler transform of period 6 sequence [-2, -1, -4, -1, -2, -6, ...].
G.f. is a period 1 Fourier series which satisfies f(-1 / (18 t)) = 34992^(1/2) (t/i)^3 g(t) where q = exp(2 Pi i t) and g(t) is g.f. for A122407.
G.f.: x * Product_{k>0} (1 - x^k)^2 * (1 - x^(3*k))^2 * (1 - x^(6*k))^3 / (1 - x^(2*k)).
EXAMPLE
G.f. = q - 2*q^2 - 2*q^4 + 6*q^5 - 4*q^7 + 4*q^8 + 6*q^10 - 24*q^11 + 8*q^13 + ...
MATHEMATICA
eta[q_]:= q^(1/24)*QPochhammer[q]; Rest[CoefficientList[Series[eta[q]^2 *eta[q^3]^2*eta[q^6]^3/eta[q^2], {q, 0, 50}], q]] (* G. C. Greubel, Aug 11 2018 *)
PROG
(PARI) {a(n) = my(A); if( n<1, 0, n--; A = x * O(x^n); polcoeff( eta(x + A)^2 * eta(x^3 + A)^2 * eta(x^6 + A)^3 / eta(x^2 + A), n))};
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Feb 25 2012
EXTENSIONS
a(40) corrected by Seiichi Manyama, Jan 09 2017
STATUS
approved