A253243 - OEIS

A253243

Expansion of phi(-x^2) * psi(x^3) * chi(x^3) in powers of x where phi(), psi(), chi() are Ramanujan theta functions.

1, 0, -2, 2, 0, -4, 1, 0, 0, 2, 0, 0, 3, 0, -4, 2, 0, 0, 2, 0, -2, 0, 0, -4, 2, 0, 0, 2, 0, -4, 1, 0, -4, 4, 0, 0, 0, 0, 0, 2, 0, 0, 3, 0, 0, 2, 0, -4, 2, 0, -4, 0, 0, 0, 4, 0, -2, 2, 0, -4, 2, 0, 0, 0, 0, 0, 0, 0, -8, 2, 0, 0, 1, 0, 0, 4, 0, -4, 2, 0, 0, 2

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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..1000

Michael Somos, Introduction to Ramanujan theta functions

Eric Weisstein's World of Mathematics, Ramanujan Theta Functions

FORMULA

Expansion q^(-1/4) * eta(q^2)^2 * eta(q^6)^4 / (eta(q^3)^2 * eta(q^4) * eta(q^12)) in powers of q.

Euler transform of period 12 sequence [ 0, -2, 2, -1, 0, -4, 0, -1, 2, -2, 0, -2, ...].

G.f. is a period 1 Fourier series which satisfies f(-1 / (144 t)) = 108^(1/2) (t/i) g(t) where q = exp(2 Pi i t) and g() is the g.f. for A246650.

a(n) = A123530(2*n) = A097109(4*n + 1) = A112848(4*n + 1) = A123477(4*n + 1). 3 * a(n) = A226535(4*n + 1). -3 * a(n) = A005928(4*n + 1).

a(3*n) = A123884(n). a(3*n + 1) = 0. a(3*n + 2) = -2 * A112605(n).

EXAMPLE

G.f. = 1 - 2*x^2 + 2*x^3 - 4*x^5 + x^6 + 2*x^9 + 3*x^12 - 4*x^14 + 2*x^15 + ...

G.f. = q - 2*q^9 + 2*q^13 - 4*q^21 + q^25 + 2*q^37 + 3*q^49 - 4*q^57 + ...

MATHEMATICA

a[ n_] := SeriesCoefficient[ EllipticTheta[ 4, 0, x^2] QPochhammer[ -x^3, x^6] EllipticTheta[ 2, 0, x^(3/2)] / (2 x^(3/8)), {x, 0, n}];

PROG

(PARI) {a(n) = if( n<0, 0, n = 4*n + 1; sumdiv(n, d, [ 0, 1, -1, -3, 1, -1, 3, 1, -1] [d%9 + 1]))};

(PARI) {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x^2 + A)^2 * eta(x^6 + A)^4 / (eta(x^3 + A)^2 * eta(x^4 + A) * eta(x^12 + A)), n))};

CROSSREFS

Cf. A005928, A097109, A112605, A112848, A123477, A123530, A123884, A226535, A246650.

Sequence in context: A191718 A286777 A286123 * A201396 A005881 A218875

Adjacent sequences: A253240 A253241 A253242 * A253244 A253245 A253246

KEYWORD

sign

AUTHOR

Michael Somos, Jun 04 2015

STATUS

approved