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 A163145 #10 Mar 23 2020 09:48:16
%S A163145 1,21,420,8400,167790,3351600,66948210,1337288400,26712295890,
%T A163145 533577313500,10658190898110,212897044846500,4252612111884990,
%U A163145 84945799915397400,1696789816099808010,33893325895893882600,677018172425014524090,13523417772619230573300
%N A163145 Number of reduced words of length n in Coxeter group on 21 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I.
%C A163145 The initial terms coincide with those of A170740, although the two sequences are eventually different.
%C A163145 Computed with MAGMA using commands similar to those used to compute A154638.
%H A163145 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (19,19,19,-190).
%F A163145 G.f.: (t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(190*t^4 - 19*t^3 - 19*t^2 - 19*t + 1).
%t A163145 coxG[{4,190,-19}] (* The coxG program is at A169452 *) (* _Harvey P. Dale_, Mar 25 2019 *)
%o A163145 (PARI) Vec((t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(190*t^4 - 19*t^3 - 19*t^2 - 19*t + 1) + O(t^20)) \\ _Jinyuan Wang_, Mar 23 2020
%K A163145 nonn
%O A163145 0,2
%A A163145 _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009
%E A163145 More terms from _Jinyuan Wang_, Mar 23 2020