OFFSET
-1,7
LINKS
Seiichi Manyama, Table of n, a(n) for n = -1..10000
FORMULA
Expansion of eta(q) * eta(q^11) / (eta(q^3) * eta(q^33)) in powers of q.
Euler transform of period 33 sequence [ -1, -1, 0, -1, -1, 0, -1, -1, 0, -1, -2, 0, -1, -1, 0, -1, -1, 0, -1, -1, 0, -2, -1, 0, -1, -1, 0, -1, -1, 0, -1, -1, 0, ...].
G.f. A(x) satisfies 0 = f(A(x), A(x^2)) where f(u, v) = u*v * (u*v + 3) - (u+v) * (u^2 - 3 * u*v + v^2).
G.f. is a period 1 Fourier series which satisfies f(-1 / (33 t)) = 3 g(t) where q = exp(2 Pi i t) and g() is the g.f. for A128663.
G.f.: 1/x * Product_{k>0} (1 - x^k) * (1 - x^(11*k)) / ((1 - x^(3*k)) * (1 - x^(33*k))).
EXAMPLE
1/q - 1 - q + q^2 - q^3 + 2*q^5 - q^6 - q^7 + 3*q^8 - 2*q^9 - 2*q^10 + ...
MATHEMATICA
a[ n_] := SeriesCoefficient[ QPochhammer[ q] QPochhammer[ q^11] / (q QPochhammer[ q^3] QPochhammer[ q^33]), {q, 0, n}] (* Michael Somos, Jul 25 2013 *)
PROG
(PARI) {a(n) = local(A); if( n<-1, 0, n++; A = x * O(x^n); polcoeff( eta(x + A) * eta(x^11 + A) / (eta(x^3 + A) * eta(x^33 + A)), n))}
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, May 22 2013
STATUS
approved