A107063 - OEIS

A107063

Expansion of q^(-1/24) * (eta(q^2) * eta(q^3)^4) / (eta(q) * eta(q^6)^2) in powers of q.

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

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OFFSET

0,4

COMMENTS

Ramanujan theta functions: f(q) := Prod_{k>=1} (1-(-q)^k) (see A121373), phi(q) := theta_3(q) := Sum_{k=-oo..oo} q^(k^2) (A000122), psi(q) := Sum_{k=0..oo} q^(k*(k+1)/2) (A010054), chi(q) := Product_{k>=0} (1+q^(2k+1)) (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

Euler transform of period 6 sequence [1, 0, -3, 0, 1, -2, ...].

G.f.: Product_{k>0} (1+x^k)*(1-x^(3*k))^2/(1+x^(3*k))^2.

Expansion of phi(-q^3)^2 / chi(-q) in powers of q where phi(), chi() are Ramanujan theta functions.

MATHEMATICA

eta[q_]:= q^(1/24)*QPochhammer[q]; CoefficientList[Series[q^(-1/24)* (eta[q^2]*eta[q^3]^4)/(eta[q]*eta[q^6]^2), {q, 0, 100}], q] (* G. C. Greubel, Apr 18 2018 *)

PROG

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

CROSSREFS

A030204(3*n) = a(n).

Sequence in context: A287401 A003406 A226289 * A290453 A108423 A361154

Adjacent sequences: A107060 A107061 A107062 * A107064 A107065 A107066

KEYWORD

sign

AUTHOR

Michael Somos, May 10 2005

STATUS

approved