OFFSET
0,2
COMMENTS
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..2500
Michael Somos, Introduction to Ramanujan theta functions
Eric Weisstein's World of Mathematics, Ramanujan Theta Functions
FORMULA
Expansion of psi(x) * psi(x^3) * f(x, x^2)^2 in powers of x where psi(), f() are Ramanujan theta functions.
Expansion of q^(-7/12) * eta(q^2)^4 * eta(q^3)^3 / eta(q)^3 in powers of q.
Euler transform of period 6 sequence [ 3, -1, 0, -1, 3, -4, ...].
G.f.: Product_{k>0} (1 - x^(2*k))^4 * (1 + x^k + x^(2*k))^3.
EXAMPLE
G.f. = 1 + 3*x + 5*x^2 + 7*x^3 + 8*x^4 + 11*x^5 + 13*x^6 + 14*x^7 + ...
G.f. = q^7 + 3*q^19 + 5*q^31 + 7*q^43 + 8*q^55 + 11*q^67 + 13*q^79 + ...
MATHEMATICA
a[ n_] := seriesCoefficient[ QPochhammer[ x^2]^4 QPochhammer[ x^3]^3 / QPochhammer[ x]^3, {x, 0, n}];
PROG
(PARI) {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x^2 + A)^4 * eta(x^3 + A)^3 / eta(x + A)^3, n))};
(PARI) q='q+O('q^99); Vec(eta(q^2)^4*eta(q^3)^3/eta(q)^3) \\ Altug Alkan, Aug 01 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Michael Somos, Jul 28 2015
STATUS
approved