A162807 - OEIS

%I #7 May 02 2021 18:54:52

%S 1,21,420,8190,159600,3108210,60532290,1178845500,22957618110,

%T 447091673490,8706955895400,169564956368010,3302218915041690,

%U 64309571936658300,1252406684472377910,24390187277913766890

%N Number of reduced words of length n in Coxeter group on 21 generators S_i with relations (S_i)^2 = (S_i S_j)^3 = I.

%C The initial terms coincide with those of A170740, 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_03">Index entries for linear recurrences with constant coefficients</a>, signature (19, 19, -190).

%F G.f.: (t^3 + 2*t^2 + 2*t + 1)/(190*t^3 - 19*t^2 - 19*t + 1).

%F a(n) = 19*a(n-1)+19*a(n-2)-190*a(n-3). - _Wesley Ivan Hurt_, May 02 2021

%K nonn

%O 0,2

%A _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009