A256279 Expansion of psi(q) * chi(-q^3) * phi(-q^9) in powers of q where phi(), psi(), chi() are Ramanujan theta functions.

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

Offset

0,10

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 of eta(q^2)^2 * eta(q^3) * eta(q^9)^2 / (eta(q) * eta(q^6) * eta(q^18)) in powers of q.

Euler transform of period 18 sequence [ 1, -1, 0, -1, 1, -1, 1, -1, -2, -1, 1, -1, 1, -1, 0, -1, 1, -2, ...].

a(n) = (-1)^n * A256269(n). a(4*n) = A256269(n).

a(3*n + 2) = a(4*n + 3) = 0. a(3*n + 1) = A258277(n). a(6*n + 4) = - A122856(n). a(12*n + 1) = A002175(n). a(12*n + 4) = - A122865(n).

Example

G.f. = 1 + q - q^4 - 4*q^9 - 2*q^10 + 2*q^13 - q^16 + 4*q^18 + 3*q^25 + ...

Mathematica

a[ n_] := SeriesCoefficient[ EllipticTheta[ 2, 0, q^(1/2)] / (2 q^(1/8)) QPochhammer[ q^3, q^6] EllipticTheta[ 4, 0, q^9], {q, 0, n}];

Prog

(PARI) {a(n) = if( n<1, n==0, (-1)^(n\3) * (n%3<2) * sumdiv(n, d, [0, 1, 2, -1][d%4 + 1] * if(d%9, 1, 4) * (-1)^((d%8==6) + n+d)))};
(PARI) {a(n) = my(A); if( n<0, 0, A = x * O(x^n); polcoeff( eta(x^2 + A)^2 * eta(x^3 + A) * eta(x^9 + A)^2 / (eta(x + A) * eta(x^6 + A) * eta(x^18 + A)), n))};

Crossrefs

Cf. A002175, A122856, A122865, A256269, A258277.

Sequence in context: A258997 A232833 A256269 * A363436 A277767 A107088

Adjacent sequences: A256276 A256277 A256278 * A256280 A256281 A256282

Keyword

sign

Author

Michael Somos, Jun 02 2015

Status

approved