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 A168849 #10 Jul 14 2017 10:35:22
%S A168849 1,28,756,20412,551124,14880348,401769396,10847773692,292889889684,
%T A168849 7908027021468,213516729579636,5764951698650172,155653695863554644,
%U A168849 4202649788315975388,113471544284531335476,3063731695682346057852
%N A168849 Number of reduced words of length n in Coxeter group on 28 generators S_i with relations (S_i)^2 = (S_i S_j)^20 = I.
%C A168849 The initial terms coincide with those of A170747, although the two sequences are eventually different.
%C A168849 First disagreement at index 20: a(20) = 43961201174298285125934967386, A170747(20) = 43961201174298285125934967764. - Klaus Brockhaus, Apr 02 2011
%C A168849 Computed with MAGMA using commands similar to those used to compute A154638.
%H A168849 <a href="/index/Rec#order_20">Index entries for linear recurrences with constant coefficients</a>, signature (26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, -351).
%F A168849 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)/(351*t^20 - 26*t^19 - 26*t^18 - 26*t^17 - 26*t^16 - 26*t^15 - 26*t^14 - 26*t^13 - 26*t^12 - 26*t^11 - 26*t^10 - 26*t^9 - 26*t^8 - 26*t^7 - 26*t^6 - 26*t^5 - 26*t^4 - 26*t^3 - 26*t^2 - 26*t + 1).
%t A168849 coxG[{20,351,-26}] (* The coxG program is at A169452 *) (* _Harvey P. Dale_, Jul 14 2017 *)
%Y A168849 Cf. A170747 (G.f.: (1+x)/(1-27*x)).
%K A168849 nonn
%O A168849 0,2
%A A168849 _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009