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%I #29 Jan 02 2017 01:52:34
%S 1,-4,2,12,-21,4,36,-68,21,112,-184,44,275,-456,112,644,-1019,240,
%T 1370,-2156,514,2828,-4340,992,5498,-8392,1930,10428,-15675,3528,
%U 19060,-28472,6399,34072,-50382,11184,59333,-87260,19312,101496,-148148,32480,170130,-247156
%N McKay-Thompson series of class 9c for the Monster group.
%C Cubic AGM theta functions: a(q) (see A004016), b(q) (A005928), c(q) (A005882).
%H Seiichi Manyama, <a href="/A058095/b058095.txt">Table of n, a(n) for n = 0..1000</a>
%H D. Ford, J. McKay and S. P. Norton, <a href="http://dx.doi.org/10.1080/00927879408825127">More on replicable functions</a>, Commun. 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 q^(1/3) * 3 * b(q) / c(q) in powers of q where b(), c() are cubic AGM theta functions.
%F Expansion of q^(1/3) * (eta(q) / eta(q^3))^4 in powers of q. - _Michael Somos_, Mar 24 2007
%F Given g.f. A(x), then B(q) = A(q^3) / q satisfies 0 = f(B(q), B(q^2)) where f(u, v) = (u+v)^3 - u*v * (u+3) * (v+3) .
%F Given g.f. A(x), then B(q) = A(q^3) / q satisfies 0 = f(B(q), B(q^2), B(q^4)) where f(u, v, w) = u^2*v^2 + v^2*w^2 - v*u^2*w^2 + u*w*v^2 - 9*u*w * (u+w).
%F G.f.: (Product_{k>0} (1 + x^k + x^(2*k)))^-4.
%F Euler transform of period 3 sequence [ -4, -4, 0, ...]. - _Michael Somos_, Mar 24 2007
%F a(n) = A112146(3*n - 1). Convolution inverse of A128758.
%e G.f. = 1 - 4*x + 2*x^2 + 12*x^3 - 21*x^4 + 4*x^5 + 36*x^6 - 68*x^7 + ...
%e T9c = 1/q - 4*q^2 + 2*q^5 + 12*q^8 - 21*q^11 + 4*q^14 + 36*q^17 - 68*q^20 + ...
%t a[0] = 1; a[n_] := Module[{A = x*O[x]^n}, SeriesCoefficient[(QPochhammer[x + A]/QPochhammer[x^3 + A])^4, n]]; Table[a[n], {n, 0, 50}] (* _Jean-François Alcover_, Nov 06 2015, adapted from _Michael Somos_'s PARI script *)
%o (PARI) {a(n) = local(A); if( n<0, 0, A = x * O(x^n); polcoeff( (eta(x + A) / eta(x^3 + A))^4, n))}; /* _Michael Somos_, Mar 24 2007 */
%Y Cf. A000521, A007240, A014708, A007241, A007267, A045478, etc.
%Y Cf. A112146, A128758.
%K sign
%O 0,2
%A _N. J. A. Sloane_, Nov 27 2000