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%I #11 May 05 2021 10:10:19
%S 1,22,462,9702,203511,4268880,89544840,1878307200,39399681090,
%T 826454197800,17335839305400,363639419173800,7627760320511100,
%U 160001156198268000,3356210592504924000,70400425902447564000
%N Number of reduced words of length n in Coxeter group on 22 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I.
%C The initial terms coincide with those of A170741, 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 (20,20,20,-210).
%F G.f.: (t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(210*t^4 - 20*t^3 - 20*t^2 - 20*t + 1).
%F a(n) = -210*a(n-4) + 20*Sum_{k=1..3} a(n-k). - _Wesley Ivan Hurt_, May 05 2021
%t CoefficientList[Series[(t^4 + 2 t^3 + 2 t^2 + 2 t + 1)/(210 t^4 - 20 t^3 - 20 t^2 - 20 t + 1), {t, 0, 16}], t] (* _Jinyuan Wang_, Mar 23 2020 *)
%K nonn
%O 0,2
%A _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009
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