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%I #8 Nov 23 2016 22:06:32
%S 1,7,42,252,1512,9072,54432,326592,1959552,11757291,70543620,
%T 423260985,2539561500,15237342540,91423896480,548542426320,
%U 3291248842560,19747458763200,118484546826660,710906046446925,4265428871616150
%N Number of reduced words of length n in Coxeter group on 7 generators S_i with relations (S_i)^2 = (S_i S_j)^9 = I.
%C The initial terms coincide with those of A003949, although the two sequences are eventually different.
%C Computed with MAGMA using commands similar to those used to compute A154638.
%H <a href="/index/Rec#order_09">Index entries for linear recurrences with constant coefficients</a>, signature (5, 5, 5, 5, 5, 5, 5, 5, -15).
%F G.f. (t^9 + 2*t^8 + 2*t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t +
%F 1)/(15*t^9 - 5*t^8 - 5*t^7 - 5*t^6 - 5*t^5 - 5*t^4 - 5*t^3 - 5*t^2 - 5*t
%F + 1)
%t coxG[{9,15,-5}] (* The coxG program is at A169452 *) (* _Harvey P. Dale_, Nov 02 2015 *)
%K nonn
%O 0,2
%A _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009