OFFSET
-1,2
COMMENTS
LINKS
Seiichi Manyama, Table of n, a(n) for n = -1..10000
Michael Somos, Introduction to Ramanujan theta functions
Eric Weisstein's World of Mathematics, Ramanujan Theta Functions
FORMULA
Expansion of (1/q) * chi(-q^4)^5 * chi(-q^8)^2 / (chi(-q)^2 * chi(-q^2)^5) = (1/q) * chi(q)^2 * chi(q^4)^2 * chi(-q^4)^7 / chi(-q^2)^7 = (1/q) * chi(-q^8)^7 / (chi(q)^5 * chi(-q)^7 * chi(q^4)^5) in powers of q where chi() is a Ramanujan theta function.
Expansion of eta(q^4)^10 / (eta(q)^2 * eta(q^2)^3 * eta(q^8)^3 * eta(q^16)^2) in powers of q.
Euler transform of period 16 sequence [2, 5, 2, -5, 2, 5, 2, -2, 2, 5, 2, -5, 2, 5, 2, 0, ...].
G.f. is a period 1 Fourier series which satisfies f(-1 / (16 t)) = f(t) where q = exp(2 Pi i t).
a(n) ~ exp(sqrt(n)*Pi) / (2^(3/2) * n^(3/4)). - Vaclav Kotesovec, May 01 2017
Expansion of (1/q) * chi(q)^2 * chi(q^2)^7 * chi(q^4)^2 in powers of q. - Michael Somos, Feb 09 2019
EXAMPLE
G.f. = 1/q + 2 + 8*q + 16*q^2 + 34*q^3 + 64*q^4 + 112*q^5 + 192*q^6 + 319*q^7 + ...
MATHEMATICA
QP = QPochhammer; s = QP[q^4]^10 / (QP[q]^2 * QP[q^2]^3 * QP[q^8]^3 * QP[q^16]^2) + O[q]^40; CoefficientList[s, q] (* Jean-François Alcover, Nov 14 2015, adapted from PARI *)
a[ n_] := SeriesCoefficient[ q^-1 QPochhammer[ -q, q^2]^2 QPochhammer[ -q^2, q^4]^7 QPochhammer[ -q^4, q^8]^2, {q, 0, n}]; (* Michael Somos, Feb 09 2019 *)
PROG
(PARI) {a(n) = my(A); if( n<-1, 0, n++; A = x * O(x^n); polcoeff( eta(x^4 + A)^10 / (eta(x + A)^2 * eta(x^2 + A)^3 * eta(x^8 + A)^3 * eta(x^16 + A)^2), n))};
CROSSREFS
KEYWORD
nonn
AUTHOR
Michael Somos, Aug 08 2012
STATUS
approved