OFFSET
1,2
FORMULA
Expansion of b(q) * b(q^2) * c(q) * c(q^2) * (b(q) * b(q^2) - c(q) * c(q^2)) / 9 in powers of q where b(), c() are cubic AGM theta functions.
Expansion of (eta(q) * eta(q^3))^6 - 8*(eta(q^2) * eta(q^6))^6 in powers of q.
Expansion of eta(q) * eta(q^2) * eta(q^3) * eta(q^6) * ((eta(q) * eta(q^2))^4 - 9*(eta(q^3) * eta(q^6))^4) in powers of q.
G.f.: x * Product_{k>0} (1 - x^k)^6 * (1 - x^(3*k))^6 - 8 * x^2 * Product_{k>0} (1 - x^(2*k))^6 * (1 - x^(6*k))^6.
G.f. is a period 1 Fourier series which satisfies f(-1 / (6*t)) = -216 (t/i)^6 f(t) where q = exp(2 Pi i t).
EXAMPLE
G.f. = q - 14*q^2 + 9*q^3 + 52*q^4 + 6*q^5 - 126*q^6 - 40*q^7 + 136*q^8 + ...
PROG
(PARI) {a(n) = my(A); if( n<1, 0, n--; A = x * O(x^n); polcoeff( (eta(x + A) * eta(x^3 + A))^6 - 8*x * (eta(x^2 + A) * eta(x^6+A))^6, n))};
(PARI) {a(n) = my(A, A1, A2); if( n<1, 0, n--; A = x * O(x^n); A1 = eta(x + A) * eta(x^2 + A); A2 = eta(x^3 + A) * eta(x^6 + A); polcoeff( A1^5*A2 - 9*x * A1*A2^5, n))};
(Magma) A := Basis( CuspForms( Gamma1(6), 6), 49); A[1] - 14*A[2] + 9*A[3]; /* Michael Somos, Feb 19 2015 */
CROSSREFS
KEYWORD
sign,mult
AUTHOR
Michael Somos, Mar 04 2007
STATUS
approved