OFFSET
0,2
COMMENTS
The q-series f_{27|3} is the g.f. for A062246. This is given on page 274 of McKay and Sebbar along with equation (8.2) which gives an expression for the g.f. A(q) of this sequence, but the left side is A(q^3) and the right side is A(q). - Michael Somos, Aug 12 2014
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
J. McKay and A. Sebbar, Fuchsian groups, automorphic functions and Schwarzians, Math. Ann., 318 (2000), 255-275.
FORMULA
Expansion of Q(q^3) - 48 * q * f(-q^3)^8 - 216 * q^2 * (f(-q) * f(-q)^9)^6 / f(-q^3)^4 in powers of q where Q(), f() are Ramanujan q-series. - Michael Somos, Aug 12 2014
Expansion of (a(q)^4 - 18 * a(q)^3*a(q^3) + 60 * a(q)^2*a(q^3)^2 - 54 * a(q)*a(q^3)^3 + 9 * a(q^3)^4) / -2 where a() is a cubic AGM theta function. - Michael Somos, Aug 12 2014
Expansion of b(q)^4 - 12 * b(q)^3*c(q^3) - 66 * b(q)^2*c(q^3)^2 - 36 * b(q)*c(q^3)^3 + 9 * c(q^3)^4 in powers of q where b(), c() are cubic AGM theta functions. - Michael Somos, Aug 12 2014
Expansion of E_4(q^3) - 48 * eta(q^3)^8 - 216*(eta(q) * eta(q^9)^6 / eta(q^3)^4 in powers of q. [McKay and Sebbar, equation (8.2)] - Michael Somos, Aug 12 2014
G.f. is a period 1 Fourier series which satisfies f(-1 / (9 t)) = 81 (t/i)^4 f(t) where q = exp(2 Pi i t).
EXAMPLE
G.f. = 1 - 48*x - 216*x^2 + 1536*x^3 - 1560*x^4 - 3024*x^5 + 13824*x^6 + ...
G.f. = 1 - 48*q^3 - 216*q^6 + 1536*q^9 - 1560*q^12 - 3024*q^15 + 13824*q^18 + ...
MATHEMATICA
QP = QPochhammer; A = x*O[x]^40; A1 = QP[x + A]^3; A3 = QP[x^3 + A]^4; A9 = x*QP[x^9 + A]^3; s = ((A1 + 3*A9)*(A1 + 9*A9)*(A1^2 + 27*A9^2) - 48*x*A3^3 - 216*(A1*A9)^2)/A3; CoefficientList[s, x] (* Jean-François Alcover, Nov 14 2015, adapted from Michael Somos's PARI script *)
eta[q_] := q^(1/24)*QPochhammer[q]; E4[q] := 1; E4[q_] := 1 + 240 *Sum[k^3* q^k/(1 - q^k), {k, 1, 500}]; CoefficientList[Series[E4[q^3] - 48*eta[q^3]^8 - 216*(eta[q]*eta[q^9])^6/eta[q^3]^4, {q, 0, 50}], q] (* G. C. Greubel, May 01 2018 *)
PROG
(PARI) {a(n) = local(A, A1, A3, A9); if( n<0, 0, A = x * O(x^n); A1 = eta(x + A)^3; A3 = eta(x^3 + A)^4; A9 = x * eta(x^9 + A)^3; polcoeff( ((A1 + 3*A9) * (A1 + 9*A9) * (A1^2 + 27*A9^2) - 48*x*A3^3 - 216*(A1*A9)^2) / A3, n))}; /* Michael Somos, Aug 12 2014 */
(Magma) A := Basis( ModularForms( Gamma0(9), 8/2), 30); A[1] - 48*A[2] - 216*A[3] + 1536*A[4] - 1560*A[5]; /* Michael Somos, Aug 12 2014 */
CROSSREFS
KEYWORD
sign
AUTHOR
N. J. A. Sloane, Jul 01 2001
EXTENSIONS
More terms from John McKay (mckay(AT)cs.concordia.ca), Apr 18 2004
More terms from Michael Somos, Aug 12 2014
STATUS
approved