OFFSET
0,4
COMMENTS
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
Michael Somos, Introduction to Ramanujan theta functions
Eric Weisstein's World of Mathematics, Ramanujan Theta Functions
FORMULA
EXAMPLE
G.f. = 1 + x + 6*x^3 + 5*x^4 + 25*x^6 + 19*x^7 + 84*x^9 + 61*x^10 + ...
G.f. = q^2 + q^3 + 6*q^5 + 5*q^6 + 25*q^8 + 19*q^9 + 84*q^11 + 61*q^12 + ...
MATHEMATICA
a[ n_] := SeriesCoefficient[ (1/2) x^(-1/8) EllipticTheta[ 2, 0, x^(1/2)] QPochhammer[ x^18]^3 / (EllipticTheta[ 4, 0, x^3] QPochhammer[ x^3]^3), {x, 0, n}];
PROG
(PARI) {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x^2 + A)^2 * eta(x^6 + A) * eta(x^18 + A)^3 / (eta(x + A) * eta(x^3 + A)^5), n))};
CROSSREFS
KEYWORD
nonn
AUTHOR
Michael Somos, Sep 07 2015
STATUS
approved