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 F - 2/F, where F = q^(1/3) * eta(q^2) * eta(q^3)^3 / (eta(q) * eta(q^6)^3), in powers of q. - G. C. Greubel, May 28 2018
EXAMPLE
T18A = 1/q - 2*q + q^2 + 2*q^4 + q^5 - q^8 - 4*q^10 - q^11 + 4*q^13 + 2*q^16 + ...
MATHEMATICA
a[ n_] := SeriesCoefficient[ 1 + 1/q QPochhammer[ q] QPochhammer[ q^2] / (QPochhammer[ q^9] QPochhammer[ q^18]), {q, 0, n}]; (* Michael Somos, Apr 26 2015 *)
PROG
(PARI) {a(n) = my(A); if( n<1, n==-1, n++; A = x * O(x^n); polcoeff( eta(x + A) * eta(x^2 + A) / (eta(x^9 + A) * eta(x^18 + A)), n))}; /* Michael Somos, Mar 17 2004 */
CROSSREFS
KEYWORD
sign
AUTHOR
N. J. A. Sloane, Nov 27 2000
STATUS
approved