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A227395 Expansion of q^2 * phi(-q) * psi(q^16) in powers of q where phi(), psi() are Ramanujan theta functions. 4
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 (list; graph; refs; listen; history; text; internal format)
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

M. 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

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Last modified September 30 21:27 EDT 2020. Contains 337440 sequences. (Running on oeis4.)