OFFSET
0,5
COMMENTS
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
D. Ford, J. McKay and S. P. Norton, More on replicable functions, Commun. Algebra 22, No. 13, 5175-5193 (1994).
Eric Weisstein's World of Mathematics, Ramanujan Theta Functions
FORMULA
Expansion of chi(-x) * chi(-x^2) * chi(-x^3) * chi(-x^6) in powers of x where chi() is a Ramanujan theta function. - Michael Somos, Mar 06 2011
Expansion of q^(1/2) * eta(q) * eta(q^3) / (eta(q^4) * eta(q^12)) in powers of q. - Michael Somos, Mar 06 2011
Euler transform of period 12 sequence [ -1, -1, -2, 0, -1, -2, -1, 0, -2, -1, -1, 0, ...]. - Michael Somos, Mar 06 2011
G.f. is a period 1 Fourier series which satisfies f(-1 / (48 t)) = 4 / f(t) where q = exp(2 Pi i t). - Michael Somos, Mar 06 2011
EXAMPLE
T24D = 1/q - q - q^3 - q^5 + 2*q^7 + q^9 - 2*q^11 + q^13 + 3*q^15 - 4*q^19 + ...
MATHEMATICA
QP = QPochhammer; s = QP[q]*(QP[q^3]/(QP[q^4]*QP[q^12])) + O[q]^70; CoefficientList[s, q] (* Jean-François Alcover, Nov 13 2015, from 2nd formula *)
eta[q_]:= q^(1/24)*QPochhammer[q]; a:= CoefficientList[Series[q^(1/2)* eta[q]*eta[q^3]/(eta[q^4]*eta[q^12]), {q, 0, 60}], q]; Table[a[[n]], {n, 1, 50}] (* G. C. Greubel, Jun 14 2018 *)
PROG
(PARI) q='q+O('q^50); A=eta(q)*eta(q^3)/(eta(q^4)*eta(q^12)); Vec(A) \\ G. C. Greubel, Jun 14 2018
CROSSREFS
KEYWORD
sign
AUTHOR
N. J. A. Sloane, Nov 27 2000
STATUS
approved