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%I #20 Jun 28 2018 04:25:32
%S 1,2,9,10,28,30,73,96,165,212,358,468,746,950,1449,1844,2727,3480,
%T 4935,6288,8715,11056,15091,18990,25468,31910,42225,52752,68785,85536,
%U 110371,136744,174816,215480,273152,335388,421909,516244,644550,785784,974921,1184430,1461239,1768900
%N McKay-Thompson series of class 20B for Monster.
%H G. C. Greubel, <a href="/A058551/b058551.txt">Table of n, a(n) for n = -1..2500</a>
%H D. Ford, J. McKay and S. P. Norton, <a href="http://dx.doi.org/10.1080/00927879408825127">More on replicable functions</a>, Comm. Algebra 22, No. 13, 5175-5193 (1994).
%H <a href="/index/Mat#McKay_Thompson">Index entries for McKay-Thompson series for Monster simple group</a>
%F Expansion of A + 4*q/A, where A = q^(1/2)*(eta(q)*eta(q^5)/(eta(q^2) *eta(q^10)))^2, in powers of q. - _G. C. Greubel_, Jun 21 2018
%F a(n) ~ exp(2*Pi*sqrt(n/5)) / (2 * 5^(1/4) * n^(3/4)). - _Vaclav Kotesovec_, Jun 28 2018
%e T20B = 1/q + 2*q + 9*q^3 + 10*q^5 + 28*q^7 + 30*q^9 + 73*q^11 + 96*q^13 + ...
%t eta[q_]:= q^(1/24)*QPochhammer[q]; A:= q^(1/2)*(eta[q]*eta[q^5]/(eta[q^2] *eta[q^10]))^2; a:= CoefficientList[Series[A + 4*q/A, {q, 0, 60}], q]; Table[a[[n]], {n, 1, 50}] (* _G. C. Greubel_, Jun 21 2018 *)
%o (PARI) q='q+O('q^50); A = (eta(q)*eta(q^5)/(eta(q^2) *eta(q^10)))^2; Vec(A + 4*q/A) \\ _G. C. Greubel_, Jun 21 2018
%Y Cf. A000521, A007240, A014708, A007241, A007267, A045478, etc.
%K nonn
%O -1,2
%A _N. J. A. Sloane_, Nov 27 2000
%E Terms a(12) onward added by _G. C. Greubel_, Jun 21 2018
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