A227395 Expansion of q^2 * phi(-q) * psi(q^16) in powers of q where phi(), psi() are Ramanujan theta functions.

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

Offset

2,2

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 = 2..1000

Michael Somos, Introduction to Ramanujan theta functions

Eric Weisstein's World of Mathematics, Ramanujan Theta Functions

Formula

Expansion of eta(q)^2 * eta(q^32)^2 / (eta(q^2) * eta(q^16)) in powers of q.

Euler transform of period 32 sequence [ -2, -1, -2, -1, -2, -1, -2, -1, -2, -1, -2, -1, -2, -1, -2, 0, -2, -1, -2, -1, -2, -1, -2, -1, -2, -1, -2, -1, -2, -1, -2, -2, ...].

G.f. is a period 1 Fourier series which satisfies f(-1 / (32 t)) = 32^(1/2) (t/i) f(t) where q = exp(2 Pi i t).

a(4*n) = a(4*n + 1) = a(8*n + 7) = 0. a(4*n + 2) = A113411(n). a(8*n + 3) = -2 * A033761(n).

G.f.: x^2 * Product_{k>0} (1 - x^k)^2 * (1 - x^(32*k))^2 / ((1 - x^(2*k)) * (1 - x^(16*k))).

a(n) = (-1)^n * A255258(n). - Michael Somos, Feb 20 2015

Example

G.f. = q^2 - 2*q^3 + 2*q^6 - 2*q^11 + 3*q^18 - 2*q^19 + 2*q^22 - 4*q^27 + 2*q^34 + ...

Mathematica

a[ n_] := SeriesCoefficient[ EllipticTheta[ 4, 0, q] EllipticTheta[ 2, 0, q^8] / 2, {q, 0, n}];

Prog

(PARI) {a(n) = local(A); if( n<2, 0, n -= 2; A = x * O(x^n); polcoeff( eta(x + A)^2 * eta(x^32 + A)^2 / (eta(x^2 + A) * eta(x^16 + A)), n))};

Crossrefs

Cf. A033761, A113411, A255258.

Sequence in context: A033731 A033729 A318984 * A255258 A329266 A260671

Adjacent sequences: A227392 A227393 A227394 * A227396 A227397 A227398

Keyword

sign

Author

Michael Somos, Jul 10 2013

Status

approved