OFFSET
-1,3
LINKS
G. C. Greubel, Table of n, a(n) for n = -1..1000
M. Koike, Mathieu group M24 and modular forms, Nagoya Math. J., 99 (1985), 147-157. MR0805086 (87e:11060)
FORMULA
Associated with permutations in Mathieu group M24 of shape (14)(7)(2)(1).
G.f. is a period 1 Fourier series which satisfies f(-1 / (14 t)) = f(t) where q = exp(2 Pi i t).
a(n) ~ exp(2*Pi*sqrt(2*n/7)) / (2^(3/4) * 7^(1/4) * n^(3/4)). - Vaclav Kotesovec, Sep 07 2017
Expansion of A - 3 + 1/A, where A = (eta(q^2)*eta(q^7)/(eta(q)*eta(q^14) ))^4, in powers of q. - G. C. Greubel, Jun 17 2018
EXAMPLE
G.f. = 1/q + 1 + 11*q + 20*q^2 + 57*q^3 + 92*q^4 + 207*q^5 + 312*q^6 + 623*q^7 + ...
MATHEMATICA
QP = QPochhammer; A = q^2*O[q]^40; A = (QP[q + A]*(QP[q^7 + A]/(QP[q^2 + A]*QP[q^14 + A])))^3/q; s = q*(4 + A + 8/A); CoefficientList[s, q] (* Jean-François Alcover, Nov 15 2015, adapted from PARI *)
a[ n_] := With[{A = (QPochhammer[ q] QPochhammer[ q^7] / (QPochhammer[ q^2] QPochhammer[ q^14]))^3 / q}, SeriesCoefficient[ 4 + A + 8 / A, {q, 0, n}]]; (* Michael Somos, May 05 2016 *)
eta[q_]:= q^(1/24)*QPochhammer[q]; A:= (eta[q^2]*eta[q^7]/(eta[q]* eta[q^14]))^4; a:= CoefficientList[Series[q*(A - 3 + 1/A), {q, 0, 60}], q]; Table[a[[n]], {n, 1, 50}] (* G. C. Greubel, Jun 17 2018 *)
PROG
(PARI) {a(n) = my(A); if( n<-1, 0, A = x^2 * O(x^n); A = (eta(x + A) * eta(x^7 + A) / (eta(x^2 + A) * eta(x^14 + A)))^3 / x; polcoeff( (4 + A + 8 / A), n))};
(PARI) q='q+O('q^50); A = (eta(q^2)*eta(q^7)/(eta(q)*eta(q^14)))^4/q; Vec(A - 3 +1/A) \\ G. C. Greubel, Jun 17 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Michael Somos, Nov 22 2007
STATUS
approved