A227401 Expansion of chi(x^6) / (chi(-x) * chi(x^3)) in powers of x which chi() is a Ramanujan theta function.

1, 1, 1, 1, 1, 2, 4, 5, 5, 5, 6, 9, 12, 15, 16, 17, 20, 26, 34, 40, 44, 48, 55, 68, 84, 98, 108, 118, 135, 161, 192, 221, 244, 268, 303, 354, 414, 470, 519, 571, 641, 737, 847, 954, 1052, 1156, 1291, 1465, 1664, 1861, 2048, 2248, 2496, 2807, 3158, 3511, 3855

Offset

0,6

Comments

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

Links

G. C. Greubel, Table of n, a(n) for n = 0..1000

Vaclav Kotesovec, A method of finding the asymptotics of q-series based on the convolution of generating functions, arXiv:1509.08708 [math.CO], 2015-2016.

Michael Somos, Introduction to Ramanujan theta functions

Eric Weisstein's World of Mathematics, Ramanujan Theta Functions

Formula

Expansion of f(x^6) / f(-x^1, -x^5) in powers of x where f(,) is a Ramanujan theta function.

Expansion of q^(1/12) * eta(q^2) * eta(q^3) * eta(q^12)^3 / (eta(q) * eta(q^6)^3 * eta(q^24)) in powers of q.

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

a(n) ~ 11^(1/4) * exp(Pi*sqrt(11*n)/6) / (4*sqrt(6)*n^(3/4)). - Vaclav Kotesovec, Jul 11 2016

Example

G.f. = 1 + x + x^2 + x^3 + x^4 + 2*x^5 + 4*x^6 + 5*x^7 + 5*x^8 + 5*x^9 + ...
G.f. = 1/q + q^11 + q^23 + q^35 + q^47 + 2*q^59 + 4*q^71 + 5*q^83 + 5*q^95 + ...

Mathematica

a[ n_] := SeriesCoefficient[ QPochhammer[ -x^6] / (QPochhammer[ x, x^6] QPochhammer[ x^5, x^6] QPochhammer[ x^6]), {x, 0, n}];
a[ n_] := SeriesCoefficient[ QPochhammer[ -x^6, x^12] QPochhammer[ -x, x] QPochhammer[ x^3, -x^3], {x, 0, n}];

Prog

(PARI) {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x^2 + A) * eta(x^3 + A) * eta(x^12 + A)^3 / (eta(x + A) * eta(x^6 + A)^3 * eta(x^24 + A)), n))};

Crossrefs

Sequence in context: A034214 A317749 A253415 * A131813 A083038 A061008

Adjacent sequences: A227398 A227399 A227400 * A227402 A227403 A227404

Keyword

nonn

Author

Michael Somos, Sep 20 2013

Status

approved