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 A168826 #12 Nov 24 2016 18:29:36
%S A168826 1,5,20,80,320,1280,5120,20480,81920,327680,1310720,5242880,20971520,
%T A168826 83886080,335544320,1342177280,5368709120,21474836480,85899345920,
%U A168826 343597383680,1374389534710,5497558138800,21990232555050,87960930219600
%N A168826 Number of reduced words of length n in Coxeter group on 5 generators S_i with relations (S_i)^2 = (S_i S_j)^20 = I.
%C A168826 The initial terms coincide with those of A003947, although the two sequences are eventually different.
%C A168826 First disagreement at index 20: a(20) = 4649045862, A003947(20) = 4649045868. - _Klaus Brockhaus_, Apr 01 2011
%C A168826 Computed with MAGMA using commands similar to those used to compute A154638.
%H A168826 G. C. Greubel, <a href="/A168826/b168826.txt">Table of n, a(n) for n = 0..1000</a>
%H A168826 <a href="/index/Rec#order_20">Index entries for linear recurrences with constant coefficients</a>, signature (3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, -6).
%F A168826 G.f.: (t^20 + 2*t^19 + 2*t^18 + 2*t^17 + 2*t^16 + 2*t^15 + 2*t^14 + 2*t^13 + 2*t^12 + 2*t^11 + 2*t^10 + 2*t^9 + 2*t^8 + 2*t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(6*t^20 - 3*t^19 - 3*t^18 - 3*t^17 - 3*t^16 - 3*t^15 - 3*t^14 - 3*t^13 - 3*t^12 - 3*t^11 - 3*t^10 - 3*t^9 - 3*t^8 - 3*t^7 - 3*t^6 - 3*t^5 - 3*t^4 - 3*t^3 - 3*t^2 - 3*t + 1).
%t A168826 CoefficientList[Series[(t^20 + 2*t^19 + 2*t^18 + 2*t^17 + 2*t^16 + 2*t^15 + 2*t^14 + 2*t^13 + 2*t^12 + 2*t^11 + 2*t^10 + 2*t^9 + 2*t^8 + 2*t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(6*t^20 - 3*t^19 - 3*t^18 - 3*t^17 - 3*t^16 - 3*t^15 - 3*t^14 - 3*t^13 - 3*t^12 - 3*t^11 - 3*t^10 - 3*t^9 - 3*t^8 - 3*t^7 - 3*t^6 - 3*t^5 - 3*t^4 - 3*t^3 - 3*t^2 - 3*t + 1), {t,0,100}], t] (* _G. C. Greubel_, Nov 22 2016 *)
%Y A168826 Cf. A003947 (G.f.: (1+x)/(1-4*x)).
%K A168826 nonn
%O A168826 0,2
%A A168826 _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009