OFFSET
-1,3
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 + 5*q^2/A, where A = q*(eta(q^3)/eta(q^15))^2, in powers of q. - G. C. Greubel, Jun 21 2018
EXAMPLE
T15a = 1/q + 5*q - 2*q^2 + 10*q^4 - q^5 + 25*q^7 + 2*q^8 + 50*q^10 + q^11 + ...
MATHEMATICA
eta[q_] := q^(1/24)*QPochhammer[q]; e15D := q^(1/3)*(eta[q]/eta[q^5])^2;
a[n_]:= SeriesCoefficient[(e15D /. {q -> q^3}) + 5*q^2/(e15D /. {q -> q^3}), {q, 0, n}]; Table[a[n], {n, 0, 50}] (* G. C. Greubel, Feb 14 2018 *)
PROG
(PARI) {a(n) = my(A); if( n<-1, 0, n++; A = x * O(x^n); A = (eta(x^3 + A) / eta(x^15 + A))^2; polcoeff( A + 5*x^2 / A, n))}; /* Michael Somos, Feb 18 2018 */
CROSSREFS
KEYWORD
sign
AUTHOR
N. J. A. Sloane, Nov 27 2000
EXTENSIONS
Terms a(24) onward added by G. C. Greubel, Feb 14 2018
STATUS
approved