OFFSET
-1,2
LINKS
G. C. Greubel, Table of n, a(n) for n = -1..1000
Michael Somos, Introduction to Ramanujan theta functions
Eric Weisstein's World of Mathematics, Ramanujan Theta Functions
FORMULA
Expansion of eta(q)^2 * eta(q^4)^12 / (eta(q^2)^9 * eta(q^8)^3 * eta(q^16)^2) in powers of q.
Euler transform of period 16 sequence [ -2, 7, -2, -5, -2, 7, -2, -2, -2, 7, -2, -5, -2, 7, -2, 0, ...].
G.f. is a period 1 Fourier series which satisfies f(-1 / (16 t)) = 2 g(t) where q = exp(2 Pi i t) and g() is the g.f. for A212318.
Apparently a(n) = A215346(n) for n <> 0. - R. J. Mathar, Nov 27 2013
EXAMPLE
G.f. = 1/q - 2 + 8*q - 16*q^2 + 34*q^3 - 64*q^4 + 112*q^5 - 192*q^6 + ...
MATHEMATICA
a[ n_]:= SeriesCoefficient[2*EllipticTheta[3, 0, q^2]^2/(EllipticTheta[3, 0, q]*EllipticTheta[2, 0, q^4]), {q, 0, n}]; Table[a[n], {n, -1, 50}] (* modified by G. C. Greubel, Mar 14 2018 *)
PROG
(PARI) {a(n) = local(A); if( n<-1, 0, n++; A = x * O(x^n); polcoeff( eta(x + A)^2 * eta(x^4 + A)^12 / (eta(x^2 + A)^9 * eta(x^8 + A)^3 * eta(x^16 + A)^2), n))};
(PARI) q='q+O('q^99); Vec(eta(q)^2*eta(q^4)^12/(eta(q^2)^9*eta(q^8)^3*eta(q^16)^2)) \\ Altug Alkan, Mar 20 2018
CROSSREFS
KEYWORD
sign
AUTHOR
Michael Somos, Nov 23 2013
EXTENSIONS
Offset corrected by Altug Alkan, Mar 22 2018
STATUS
approved