%I #18 Jun 22 2018 04:29:54
%S 1,-3,0,-2,-6,0,-1,-15,0,4,-24,0,-3,-48,0,0,-78,0,7,-132,0,-8,-204,0,
%T -3,-324,0,14,-486,0,-14,-735,0,-4,-1068,0,26,-1563,0,-26,-2220,0,-7,
%U -3159,0,44,-4404,0,-41,-6135,0,-10,-8412,0,73,-11508,0,-72,-15552,0,-20,-20964,0,118,-27978,0,-109
%N McKay-Thompson series of class 18f for the Monster group.
%H G. C. Greubel, <a href="/A058544/b058544.txt">Table of n, a(n) for n = 0..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 - 3*q/A, where q^(1/2)*(eta(q^3)/eta(q^9))^2, in powers of q. - _G. C. Greubel_, Jun 21 2018
%e T18f = 1/q - 3*q - 2*q^5 - 6*q^7 - q^11 - 15*q^13 + 4*q^17 - 24*q^19 + ...
%t eta[q_]:= q^(1/24)*QPochhammer[q]; A:= q^(1/2)*(eta[q^3]/eta[q^9])^2; a:= CoefficientList[Series[A - 3*q/A, {q, 0, 60}], q]; Table[a[[n]], {n, 1, 50}] (* _G. C. Greubel_, Jun 21 2018 *)
%o (PARI) q='q+O('q^60); A = (eta(q^3)/eta(q^9))^2; Vec(A - 3*q/A) \\ _G. C. Greubel_, Jun 21 2018
%Y Cf. A000521, A007240, A014708, A007241, A007267, A045478, etc.
%K sign
%O 0,2
%A _N. J. A. Sloane_, Nov 27 2000