OFFSET
-1,2
LINKS
G. C. Greubel, Table of n, a(n) for n = -1..1000
J. H. Conway and S. P. Norton, Monstrous Moonshine, Bull. Lond. Math. Soc. 11 (1979) 308-339.
N. D. Elkies, Elliptic and modular curves over finite fields and related computational issues, in AMS/IP Studies in Advanced Math., 7 (1998), 21-76, esp. p. 66.
D. Ford, J. McKay and S. P. Norton, More on replicable functions, Comm. Algebra 22, No. 13, 5175-5193 (1994).
J. McKay and H. Strauss, The q-series of monstrous moonshine and the decomposition of the head characters, Comm. Algebra 18 (1990), no. 1, 253-278.
FORMULA
Expansion of -7 + (h+7)^2/h, where h = (eta(q)/eta(q^7))^4.
a(n) ~ exp(4*Pi*sqrt(n/7)) / (sqrt(2) * 7^(1/4) * n^(3/4)). - Vaclav Kotesovec, Sep 07 2017
EXAMPLE
1/q + 3 + 51*q + 204*q^2 + 681*q^3 + 1956*q^4 + 5135*q^5 + 12360*q^6 + ...
MATHEMATICA
QP = QPochhammer; h = q*(QP[q^7]/QP[q])^4; s = 1 - 7*q + q*((1+7*h)^2/h - 1/q) + O[q]^30; CoefficientList[s, q] (* Jean-François Alcover, Nov 15 2015 *)
eta[q_]:= q^(1/24)*QPochhammer[q]; h:= (eta[q]/eta[q^7])^4; A045489 := CoefficientList[Series[q*(h + 7 + 49/h), {q, 0, 50}], q]; Table[ A045489[[n]], {n, 1, 30}] (* G. C. Greubel, May 28 2018 *)
PROG
(PARI) q='q+O('q^30); {h =(eta(q)/eta(q^7))^4/q}; Vec(h + 7 + 49/h) \\ G. C. Greubel, May 28 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved