OFFSET
-1,3
COMMENTS
Also character of extremal vertex operator algebra of rank 12.
LINKS
Seiichi Manyama, Table of n, a(n) for n = -1..10000 (terms -1..1000 from T. D. Noe)
D. Ford, J. McKay and S. P. Norton, More on replicable functions, Commun. Algebra 22, No. 13, 5175-5193 (1994).
G. Hoehn (gerald(AT)math.ksu.edu), Selbstduale Vertexoperatorsuperalgebren und das Babymonster, Doctoral Dissertation, Univ. Bonn, Jul 15 1995 (pdf, ps).
G. Hoehn, Selbstduale Vertexoperatorsuperalgebren und das Babymonster, arXiv:0706.0236 [math.QA], 2007, from Bonner Mathematische Schriften, Vol. 286 (1996), 1-85.
FORMULA
G.f.: (1/x)(Product_{k>0} (1+x^k)/(1+x^(2k)))^24 -24.
a(n) = -(-1)^n * A007246(n).
a(n) ~ exp(2*Pi*sqrt(n)) / (2*n^(3/4)). - Vaclav Kotesovec, Sep 06 2015
EXAMPLE
T4A = 1/q + 276q + 2048q^2 + 11202q^3 + 49152q^4 + 184024q^5 +...
MATHEMATICA
a[0] = 0; a[n_] := SeriesCoefficient[ Product[1 - q^k, {k, 1, n+1, 2}]^24/q, {q, 0, n}] // Abs; Table[a[n], {n, -1, 20}] (* Jean-François Alcover, Oct 14 2013, after Michael Somos *)
QP = QPochhammer; s = (QP[q^2]^2/QP[q]/QP[q^4])^24 - 24*q + O[q]^30; CoefficientList[s, q] (* Jean-François Alcover, Nov 15 2015, after Michael Somos *)
PROG
(PARI) {a(n) = my(A); if( n<-1, 0, n++; A = x * O(x^n); polcoeff( (eta(x^2 + A)^2 / (eta(x + A) * eta(x^4 + A)))^24 - 24*x, n))};
(PARI) q='q+O('q^66); Vec(+40*q+(eta(q)^4 / eta(q^4)^4 - q*4^2*eta(q^4)^4 / eta(q)^4)^2) \\ Joerg Arndt, Mar 23 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
Michael Somos, May 11 2005
STATUS
approved