This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A163969 #12 Aug 23 2017 14:47:58
%S A163969 1,20,380,7220,137180,2606420,49521790,940910400,17877229200,
%T A163969 339666055200,6453630356400,122618507616000,2329742730783510,
%U A163969 44264942521047180,841030689999256020,15979521970107624780
%N A163969 Number of reduced words of length n in Coxeter group on 20 generators S_i with relations (S_i)^2 = (S_i S_j)^6 = I.
%C A163969 The initial terms coincide with those of A170739, although the two sequences are eventually different.
%C A163969 Computed with MAGMA using commands similar to those used to compute A154638.
%H A163969 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (18, 18, 18, 18, 18, -171).
%F A163969 G.f.: (t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(171*t^6 - 18*t^5 - 18*t^4 - 18*t^3 - 18*t^2 - 18*t + 1).
%t A163969 coxG[{6,171,-18}] (* The coxG program is at A169452 *) (* _Harvey P. Dale_, May 21 2015 *)
%t A163969 CoefficientList[Series[(t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(171*t^6 - 18*t^5 - 18*t^4 - 18*t^3 - 18*t^2 - 18*t + 1), {t,0,50}], t] (* _G. C. Greubel_, Aug 23 2017 *)
%o A163969 (PARI) t='t+O('t^50); Vec((t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(171*t^6 - 18*t^5 - 18*t^4 - 18*t^3 - 18*t^2 - 18*t + 1)) \\ _G. C. Greubel_, Aug 23 2017
%K A163969 nonn,easy
%O A163969 0,2
%A A163969 _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009