OFFSET
-1,3
COMMENTS
LINKS
G. C. Greubel, Table of n, a(n) for n = -1..1000
D. Ford, J. McKay and S. P. Norton, More on replicable functions, Commun. Algebra 22, No. 13, 5175-5193 (1994).
Michael Somos, Introduction to Ramanujan theta functions
Eric Weisstein's World of Mathematics, Ramanujan Theta Functions
FORMULA
Expansion of q^(-1) * f(q^3) * phi(q^3) / (phi(-q^2) * psi(q^9)) in powers of q where f(), phi(), psi() are Ramanujan theta functions. - Michael Somos, Feb 13 2011
Expansion of eta(q^4) * eta(q^6)^8 * eta(q^9) / (eta(q^2)^2 * eta(q^3)^3 * eta(q^12)^3 * eta(q^18)^2) in powers of q. - Michael Somos, Feb 13 2011
Euler transform of period 36 sequence [ 0, 2, 3, 1, 0, -3, 0, 1, 2, 2, 0, -1, 0, 2, 3, 1, 0, -2, 0, 1, 3, 2, 0, -1, 0, 2, 2, 1, 0, -3, 0, 1, 3, 2, 0, 0, ...]. - Michael Somos, Feb 13 2011
G.f. is a period 1 Fourier series which satisfies f(-1 / (36 t)) = f(t) where q = exp(2 Pi i t). - Michael Somos, Feb 13 2011
a(n) ~ exp(2*Pi*sqrt(n)/3) / (2*sqrt(3)*n^(3/4)). - Vaclav Kotesovec, Dec 03 2015
EXAMPLE
T36D = 1/q + 2*q + 3*q^2 + 4*q^3 + 6*q^4 + 9*q^5 + 12*q^6 + 16*q^7 + ...
MATHEMATICA
a[ n_] := SeriesCoefficient[ 2 q^(1/8) QPochhammer[ -q^3] EllipticTheta[ 3, 0, q^3] / (EllipticTheta[ 4, 0, q^2] EllipticTheta[ 2, 0, q^(9/2)]), {q, 0, n}]; (* Michael Somos, Aug 26 2015 *)
nmax = 60; CoefficientList[Series[Product[(1+x^(2*k)) * (1-x^(3*k))^2 * (1+x^(3*k))^5 / ((1-x^(2*k)) * (1+x^(6*k))^3 * (1-x^(9*k)) * (1+x^(9*k))^2), {k, 1, nmax}], {x, 0, nmax}], x] (* Vaclav Kotesovec, Dec 03 2015 *)
PROG
(PARI) {a(n) = my(A); if( n<-1, 0, n++; A = x * O(x^n); polcoeff( eta(x^4 + A) * eta(x^6 + A)^8 * eta(x^9 + A) / (eta(x^2 + A)^2 * eta(x^3 + A)^3 * eta(x^12 + A)^3 * eta(x^18 + A)^2), n))} /* Michael Somos, Feb 13 2011 */
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Nov 27 2000
STATUS
approved