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A260942 Expansion of x * phi(-x) * psi(x^12) / chi(-x^3) in powers of x where phi(), psi(), chi() are Ramanujan theta functions. 2
0, 1, -2, 0, 1, 0, 0, 1, 0, 0, 0, -2, 0, 1, -2, 0, 2, 0, 0, 1, 0, 0, 1, -2, 0, 0, 0, 0, 1, -2, 0, 0, 0, 0, 1, 0, 0, 2, -2, 0, 1, -2, 0, 1, 0, 0, 1, -2, 0, 1, 0, 0, 1, 0, 0, 0, -2, 0, 2, 0, 0, 0, 0, 0, 0, -2, 0, 1, -2, 0, 0, 0, 0, 2, -2, 0, 1, 0, 0, 3, 0, 0, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

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

Michael Somos, Introduction to Ramanujan theta functions

Eric Weisstein's World of Mathematics, Ramanujan Theta Functions

FORMULA

Expansion of q^(-5/8) * eta(q)^2 * eta(q^6) * eta(q^24)^2 / (eta(q^2) * eta(q^3) * eta(q^12)) in powers of q.

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

a(3*n) = 0. a(3*n + 1) = A131963(n). a(3*n + 2) = -2 * A112609(n).

EXAMPLE

G.f. = x - 2*x^2 + x^4 + x^7 - 2*x^11 + x^13 - 2*x^14 + 2*x^16 + x^19 + ...

G.f. = q^13 - 2*q^21 + q^37 + q^61 - 2*q^93 + q^109 - 2*q^117 + 2*q^133 + ...

MATHEMATICA

a[ n_] := SeriesCoefficient[ EllipticTheta[ 4, 0, x] EllipticTheta[ 2, 0, x^6] QPochhammer[ -x^3, x^3] / (2 x^(1/2)), {x, 0, n}];

eta[q_] := q^(1/24)*QPochhammer[q]; CoefficientList[Series[ q^(-5/8)* eta[q]^2*eta[q^6]*eta[q^24]^2/(eta[q^2]*eta[q^3]*eta[q^12]), {q, 0, 50}], q] (* G. C. Greubel, Aug 01 2018 *)

PROG

(PARI) {a(n) = my(A); if( n<1, 0, n--; A = x * O(x^n); polcoeff( eta(x + A)^2 * eta(x^6 + A) * eta(x^24 + A)^2 / (eta(x^2 + A) * eta(x^3 + A) * eta(x^12 + A)), n))};

CROSSREFS

Cf. A112609, A131963.

Sequence in context: A322353 A133988 A089812 * A260162 A123858 A193261

Adjacent sequences:  A260939 A260940 A260941 * A260943 A260944 A260945

KEYWORD

sign

AUTHOR

Michael Somos, Aug 04 2015

STATUS

approved

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Last modified August 2 02:10 EDT 2021. Contains 346408 sequences. (Running on oeis4.)