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%I #8 Jun 11 2017 10:28:43
%S 1,4,12,36,108,324,972,2916,8748,26238,78696,236040,707976,2123496,
%T 6369192,19103688,57299400,171863208,515484678,1546139268,4637473692,
%U 13909589316,41720274396,125135347716,375329632284,1125759710916
%N Number of reduced words of length n in Coxeter group on 4 generators S_i with relations (S_i)^2 = (S_i S_j)^9 = I.
%C The initial terms coincide with those of A003946, 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 (2, 2, 2, 2, 2, 2, 2, 2, -3).
%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)/(3*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)
%t coxG[{9,3,-2,30}] (* The coxG program is at A169452 *) (* _Harvey P. Dale_, Jun 11 2017 *)
%K nonn
%O 0,2
%A _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009
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