OFFSET
-1,3
COMMENTS
LINKS
G. C. Greubel, Table of n, a(n) for n = -1..1000
J. H. Conway and S. P. Norton, Monstrous Moonshine, Bull. Lond. Math. Soc. 11 (1979) 308-339.
D. Ford, J. McKay and S. P. Norton, More on replicable functions, Comm. Algebra 22, No. 13, 5175-5193 (1994).
J. McKay and H. Strauss, The q-series of monstrous moonshine and the decomposition of the head characters, Comm. Algebra 18 (1990), no. 1, 253-278.
Morris Newman, Construction and application of a class of modular functions. II. Proc. London Math. Soc. (3) 9 1959 373-387.
Michael Somos, Introduction to Ramanujan theta functions
Eric Weisstein's World of Mathematics, Ramanujan Theta Functions
FORMULA
Expansion of (1/q) * a(q^2) * psi(q) / psi(q^3)^3 in powers of q where psi() is a Ramanujan theta function and a() is a cubic AGM theta function. - Michael Somos, May 22 2015
Expansion of 6 + eta(q)^5 * eta(q^3) / (eta(q^2) * eta(q^6)^5) in powers of q. - Michael Somos, May 22 2015
EXAMPLE
G.f. = 1/q + 1 + 6*q + 4*q^2 - 3*q^3 - 12*q^4 - 8*q^5 + 12*q^6 + 30*q^7 + ...
MATHEMATICA
a[ n_] := SeriesCoefficient[ 6 + QPochhammer[ q]^5 QPochhammer[ q^3] / (q QPochhammer[ q^2] QPochhammer[ q^6]^5), {q, 0, n}]; (* Michael Somos, May 22 2015 *)
a[ n_] := SeriesCoefficient[ -2 + (1/q) (QPochhammer[ q^2] QPochhammer[ q^3]^3 / (QPochhammer[ q] QPochhammer[ q^6]^3))^3, {q, 0, n}]; (* Michael Somos, May 22 2015 *)
a[ n_] := SeriesCoefficient[ (EllipticTheta[ 3, 0, q]^3 / EllipticTheta[ 3, 0, q^3] + 3 EllipticTheta[ 3, 0, q^3]^3 / EllipticTheta[ 3, 0, q]) EllipticTheta[ 2, 0, q^(1/2)] / EllipticTheta[ 2, 0, q^(3/2)]^3, {q, 0, n}]; (* Michael Somos, May 22 2015 *)
PROG
(PARI) {a(n) = my(A); if( n<-1, 0, n++; A = x * O(x^n); polcoeff( 6*x + eta(x + A)^5 * eta(x^3 + A) / (eta(x^2 + A) * eta(x^6 + A)^5), n))}; /* Michael Somos, May 22 2015 */
(PARI) {a(n) = my(A); if( n<-1, 0, n++; A = x * O(x^n); polcoeff( -2*x + (eta(x^2 + A) * eta(x^3 + A)^3 / (eta(x + A) * eta(x^6 + A)^3))^3, n))}; /* Michael Somos, May 22 2015 */
CROSSREFS
KEYWORD
sign
AUTHOR
STATUS
approved