OFFSET
-1,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = -1..10000 (terms -1..148 from G. A. Edgar)
FORMULA
Expansion of 9 * b(q) * b(q^2) / (c(q) * c(q^2)) in powers of q where b(), c() are cubic AGM theta functions.
Expansion of (eta(q) * eta(q^2) / (eta(q^3) * eta(q^6)))^4 in powers of q.
Euler transform of period 6 sequence [ -4, -8, 0, -8, -4, 0, ...].
G.f. A(x) satisfies 0 = f(A(x), A(x^2)) where f(u,v) = (u^2 + u*v + v^2)^2 - u*v * (9 + u + v) * (u*v + 9*(u+v)).
EXAMPLE
T6D = 1/q - 4 - 2*q + 28*q^2 - 27*q^3 - 52*q^4 + 136*q^5 - 108*q^6 + ...
MATHEMATICA
a[ n_] := SeriesCoefficient[ 1/q (QPochhammer[ q] QPochhammer[ q^2] / (QPochhammer[ q^3] QPochhammer[ q^6]))^4, {q, 0, n}]; (* Michael Somos, Apr 26 2015 *)
PROG
(PARI) {a(n) = my(A); if( n<-1, 0, n++; A = x * O(x^n); polcoeff( (eta(x + A) * eta(x^2 + A) / (eta(x^3+A) * eta(x^6 + A)))^4, n))};
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Aug 14 2006
STATUS
approved