OFFSET
-1,3
COMMENTS
LINKS
G. C. Greubel, Table of n, a(n) for n = -1..1000
D. Ford, J. McKay and S. P. Norton, More on replicable functions, Commun. Algebra 22, No. 13, 5175-5193 (1994).
Michael Somos, Introduction to Ramanujan theta functions
Eric Weisstein's World of Mathematics, Ramanujan Theta Functions
FORMULA
Expansion of -5 + (1/q) * (phi(q)^3 * psi(-q)) / (phi(q^3) * psi(-q^3)^3) in powers of q where phi(), psi() are Ramanujan theta functions.
a(n) = -(-1)^n * A007258(n). - Michael Somos, May 20 2015
EXAMPLE
T12B = 1/q + 6*q - 4*q^2 - 3*q^3 + 12*q^4 - 8*q^5 - 12*q^6 + 30*q^7 + ...
MATHEMATICA
a[ n_] := SeriesCoefficient[ -5 + 2 EllipticTheta[3, 0, q]^3 EllipticTheta[2, Pi/4, q^(1/2)] / (EllipticTheta[3, 0, q^3] EllipticTheta[2, Pi/4, q^(3/2)]^3), {q, 0, n}]; (* Michael Somos, May 20 2015 *)
QP = QPochhammer; s = -5*q +QP[q^2]^14/(QP[q]^5*QP[q^3]*QP[q^4]^5* QP[q^6]^2*QP[q^12]) + O[q]^50; CoefficientList[s, q] (* Jean-François Alcover, Nov 16 2015, adapted from PARI *)
PROG
(PARI) {a(n) = my(A); if( n<-1, 0, n++; A =x * O(x^n); polcoeff( -5 * x + eta(x^2 + A)^14 / (eta(x + A)^5 * eta(x^3 + A) * eta(x^4 + A)^5 * eta(x^6 + A)^2 * eta(x^12 + A)), n))}; /* Michael Somos, May 20 2015 */
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Aug 28 2005
STATUS
approved