OFFSET
-1,2
COMMENTS
LINKS
G. A. Edgar, Table of n, a(n) for n = -1..1000
D. Alexander, C. Cummins, J. McKay and C. Simons, Completely Replicable Functions, LMS Lecture Notes, 165, ed. Liebeck and Saxl (1992), 87-98, annotated and scanned copy.
Michael Somos, Introduction to Ramanujan theta functions
Eric Weisstein's World of Mathematics, Ramanujan Theta Functions
FORMULA
Expansion of (1/q) * (chi(q) * chi(q^3))^6 in powers of q where chi() is a Ramanujan theta function.
Euler transform of period 12 sequence [ 6, -6, 12, 0, 6, -12, 6, 0, 12, -6, 6, 0, ...].
G.f. is a period 1 Fourier series which satisfies f(-1 / (12 t)) = f(t) where q = exp(2 Pi i t).
G.f.: (1/x) * (Product_{k>0} (1 + x^(2*k - 1)) * (1 + x^(6*k - 3)))^6.
a(n) = -(-1)^n * A121666(n).
a(n) ~ exp(2*Pi*sqrt(n/3)) / (2*3^(1/4)*n^(3/4)). - Vaclav Kotesovec, Sep 02 2015
Expansion of eta(q^2)^12 * eta(q^6)^12 / (eta(q)^6 * eta(q^3)^6 * eta(q^4)^6 * eta(q^12)^6) in powers of q. - G. A. Edgar, Mar 11 2017
EXAMPLE
G.f. = 1/q + 6 + 15*q + 32*q^2 + 87*q^3 + 192*q^4 + 343*q^5 + 672*q^6 + 1290*q^7 + ...
MATHEMATICA
a[ n_] := SeriesCoefficient[ (1/q) (QPochhammer[ -q, q^2] QPochhammer[ -q^3, q^6])^6, {q, 0, n}]; (* Michael Somos, Sep 02 2015 *)
PROG
(PARI) {a(n) = my(A); if( n<-1, 0, n++; A = x * O(x^n); polcoeff( (eta(x^2 + A) * eta(x^6 + A))^12 / (eta(x + A) * eta(x^3 + A) * eta(x^4 + A) * eta(x^12 + A))^6, n))}
(PARI) q='q+O('q^50); Vec( eta(q^2)^12 * eta(q^6)^12 / (eta(q)^6 * eta(q^3)^6 * eta(q^4)^6 * eta(q^12)^6) ) \\ Joerg Arndt, Mar 11 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Michael Somos, Feb 27 2011
STATUS
approved