OFFSET
-1,4
COMMENTS
LINKS
G. C. Greubel, Table of n, a(n) for n = -1..5000
Michael Somos, Introduction to Ramanujan theta functions
Eric Weisstein's World of Mathematics, Ramanujan Theta Functions
FORMULA
Expansion of (1/q) * psi(q) * phi(-q^4) / (psi(-q^3) * psi(-q^6)) in powers of q where phi(), psi() are Ramanujan theta functions.
Expansion of eta(q^2)^2 * eta(q^4)^2 / (eta(q) * eta(q^3) * eta(q^8)* eta(q^24)) in powers of q.
Euler transform of period 24 sequence [ 1, -1, 2, -3, 1, 0, 1, -2, 2, -1, 1, -2, 1, -1, 2, -2, 1, 0, 1, -3, 2, -1, 1, 0, ...].
a(n) = A058573(n) unless n = 0.
EXAMPLE
1/q + 1 + 2*q^2 - q^3 - 2*q^4 + 4*q^5 - 2*q^6 - 2*q^7 + 6*q^8 - 4*q^9 + ...
MATHEMATICA
QP = QPochhammer; s=QP[q^2]^2*(QP[q^4]^2/(QP[q]*QP[q^3]*QP[q^8]*QP[q^24]))+ O[q]^60; CoefficientList[s, q] (* Jean-François Alcover, Nov 14 2015, adapted from PARI *)
PROG
(PARI) {a(n) = local(A); if( n<-1, 0, n++; A = x * O(x^n); polcoeff( eta(x^2 + A)^2 * eta(x^4 + A)^2 / (eta(x + A) * eta(x^3 + A) * eta(x^8 + A)* eta(x^24 + A)), n))}
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Feb 05 2012
STATUS
approved