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A279320 Expansion of chi(-x^4) * psi(x^6) / phi(-x) in powers of x where phi(), psi(), chi() are Ramanujan theta functions. 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

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..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

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

EXAMPLE

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 + ...

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 *)

PROG

(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))};

CROSSREFS

Cf. A131945.

Sequence in context: A179001 A222147 A003241 * A182844 A191630 A125513

Adjacent sequences:  A279317 A279318 A279319 * A279321 A279322 A279323

KEYWORD

nonn

AUTHOR

Michael Somos, Dec 09 2016

STATUS

approved

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Last modified January 20 16:32 EST 2022. Contains 350472 sequences. (Running on oeis4.)