%I #9 Mar 23 2020 06:48:08

%S 1,18,306,5202,88281,1498176,25424928,431474688,7322358456,

%T 124264377216,2108833575552,35788044422016,607342437246528,

%U 10306929088604160,174914151758088192,2968387598501627904,50375140298107596288,854893330417826832384,14508001408391876911104

%N Number of reduced words of length n in Coxeter group on 18 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I.

%C The initial terms coincide with those of A170737, 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_04">Index entries for linear recurrences with constant coefficients</a>, signature (16,16,16,-136).

%F G.f.: (t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(136*t^4 - 16*t^3 - 16*t^2 - 16*t + 1).

%o (PARI) Vec((t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(136*t^4 - 16*t^3 - 16*t^2 - 16*t + 1) + O(t^20)) \\ _Jinyuan Wang_, Mar 23 2020

%K nonn

%O 0,2

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

%E More terms from _Jinyuan Wang_, Mar 23 2020