A279320 Expansion of chi(-x^4) * psi(x^6) / phi(-x) in powers of x where phi(), psi(), chi() are Ramanujan theta functions.

1, 2, 4, 8, 15, 26, 45, 74, 119, 188, 291, 442, 664, 982, 1435, 2076, 2972, 4214, 5929, 8272, 11457, 15762, 21543, 29264, 39532, 53110, 70988, 94430, 125033, 164826, 216388, 282940, 368552, 478326, 618621, 797376, 1024485, 1312184, 1675657, 2133664, 2709307

Offset: 0

Author

Michael Somos, Dec 09 2016

Keywords

• nonn

Comments

Ramanujan theta functions: f(q) (see A121373), phi(q) (A000122), psi(q) (A010054), chi(q) (A000700).

Examples

			G.f. = 1 + 2*x + 4*x^2 + 8*x^3 + 15*x^4 + 26*x^5 + 45*x^6 + 74*x^7 + ...
G.f. = q^11 + 2*q^23 + 4*q^35 + 8*q^47 + 15*q^59 + 26*q^71 + 45*q^83 + ...
		

Links

• G. C. Greubel, Table of n, a(n) for n = 0..2500
• Vaclav Kotesovec, A method of finding the asymptotics of q-series based on the convolution of generating functions, arXiv:1509.08708 [math.CO], Sep 30 2015.
• Michael Somos, Introduction to Ramanujan theta functions
• Eric Weisstein's World of Mathematics, Ramanujan Theta Functions

Crossrefs

Cf. A131945.

Programs

Mathematica

a[ n_] := SeriesCoefficient[ x^(-3/4)/2 QPochhammer[ -x^4, x^4] EllipticTheta[ 2, 0, x^3] / EllipticTheta[ 4, 0, x], {x, 0, n}];
a[ n_] := SeriesCoefficient[ 2^(-3/2)/x EllipticTheta[ 2, Pi/4, x] EllipticTheta[ 2, 0, x^3] / QPochhammer[ x]^2, {x, 0, n}];
nmax = 50; CoefficientList[Series[Product[(1+x^k) * (1+x^(4*k)) * (1+x^(6*k)) * (1-x^(12*k)) / (1-x^k), {k, 1, nmax}], {x, 0, nmax}], x] (* Vaclav Kotesovec, Dec 10 2016 *)

PARI

{a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x^2 + A) * eta(x^8 + A) * eta(x^12 + A)^2 / (eta(x + A)^2 * eta(x^4 + A) * eta(x^6 + A)), n))};

Formula

Expansion of f(-x^2, -x^10) * f(-x^8) / f(-x)^2 in powers of x where f(, ) is Ramanujan's general theta function.

Expansion of q^(-11/12) * eta(q^2) * eta(q^8) * eta(q^12)^2 / (eta(q)^2 * eta(q^4) * eta(q^6)) in powers of q.

Euler transform of period 24 sequence [ 2, 1, 2, 2, 2, 2, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 2, 2, 2, 2, 2, 1, 2, 0, ...].

a(n) ~ exp(sqrt(13*n/3)*Pi/2) * 13^(1/4) / (16*sqrt(2)*3^(3/4)*n^(3/4)). - Vaclav Kotesovec, Dec 10 2016