OFFSET
-1,4
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).
FORMULA
Expansion of A + q^2/A, where A = q*(eta(q^6)*eta(q^15)/(eta(q^3) *eta(q^30)))^2, in powers of q. - G. C. Greubel, Jun 23 2018
EXAMPLE
T30b = 1/q + q + 2*q^2 - 2*q^4 + 3*q^5 + q^7 + 6*q^8 - 2*q^10 + 9*q^11 + ...
MATHEMATICA
nmax = 80; QP = QPochhammer; A = x^2*O[x]^(nmax+1); A = (QP[x^3 + A] * (QP[x^30 + A]/QP[x^6 + A]/QP[x^15 + A]))^2*x; a[n_] := SeriesCoefficient[ 1/A + A, n]; Table[a[n], {n, -1, nmax}] (* Jean-François Alcover, Nov 14 2015, adapted from PARI *)
eta[q_]:= q^(1/24)*QPochhammer[q]; A := q*(eta[q^6]*eta[q^15]/(eta[q^3]* eta[q^30]))^2; a:= CoefficientList[Series[A + q^2/A, {q, 0, 60}], q]; Table[a[[n]], {n, 1, 50}] (* G. C. Greubel, Jun 23 2018 *)
PROG
(PARI) a(n)=local(A); if(n<-1, 0, A=x^2*O(x^n); A=(eta(x^3+A)*eta(x^30+A)/eta(x^6+A)/eta(x^15+A))^2*x; polcoeff(1/A+A, n)) \\ Michael Somos, May 02 2004
(PARI) q='q+O('q^80); A = (eta(q^6)*eta(q^15)/(eta(q^3) *eta(q^30)))^2; Vec(A+ q^2/A) \\ G. C. Greubel, Jun 23 2018
CROSSREFS
KEYWORD
sign
AUTHOR
N. J. A. Sloane, Nov 27 2000
STATUS
approved