OFFSET
-1,3
LINKS
Seiichi Manyama, Table of n, a(n) for n = -1..10000
D. Ford, J. McKay and S. P. Norton, More on replicable functions, Commun. Algebra 22, No. 13, 5175-5193 (1994).
FORMULA
Expansion of -2 + (eta(q^3)*eta(q^7)/(eta(q)*eta(q^21)))^2 in powers of q. - G. C. Greubel, Jun 14 2018
a(n) ~ exp(4*Pi*sqrt(n/21)) / (sqrt(2) * 21^(1/4) * n^(3/4)). - Vaclav Kotesovec, Jun 28 2018
EXAMPLE
T21D = 1/q + 5*q + 8*q^2 + 16*q^3 + 26*q^4 + 44*q^5 + 66*q^6 + 104*q^7 + ...
MATHEMATICA
eta[q_]:= q^(1/24)*QPochhammer[q]; a:= CoefficientList[Series[q*(-2 + (eta[q^3]*eta[q^7]/(eta[q]*eta[q^21]))^2), {q, 0, 60}], q]; Table[a[[n]], {n, 1, 50}] (* G. C. Greubel, Jun 14 2018 *)
PROG
(PARI) q='q+O('q^50); A = -2+(eta(q^3)*eta(q^7)/(eta(q)*eta(q^21)))^2/q; Vec(A) \\ G. C. Greubel, Jun 14 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Nov 27 2000
EXTENSIONS
More terms from Michel Marcus, Feb 18 2014
STATUS
approved