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 A168882 #10 May 13 2019 13:55:24
%S A168882 1,13,156,1872,22464,269568,3234816,38817792,465813504,5589762048,
%T A168882 67077144576,804925734912,9659108818944,115909305827328,
%U A168882 1390911669927936,16690940039135232,200291280469622784
%N A168882 Number of reduced words of length n in Coxeter group on 13 generators S_i with relations (S_i)^2 = (S_i S_j)^21 = I.
%C A168882 The initial terms coincide with those of A170732, although the two sequences are eventually different.
%C A168882 First disagreement at index 21: a(21) = 49838879901817176588210, A170732(21) = 49838879901817176588210. - Klaus Brockhaus, Apr 05 2011
%C A168882 Computed with MAGMA using commands similar to those used to compute A154638.
%H A168882 <a href="/index/Rec#order_21">Index entries for linear recurrences with constant coefficients</a>, signature (11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, -66).
%F A168882 G.f.: (t^21 + 2*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)/(66*t^21 - 11*t^20 - 11*t^19 - 11*t^18 - 11*t^17 - 11*t^16 - 11*t^15 - 11*t^14 - 11*t^13 - 11*t^12 - 11*t^11 - 11*t^10 - 11*t^9 - 11*t^8 - 11*t^7 - 11*t^6 - 11*t^5 - 11*t^4 - 11*t^3 - 11*t^2 - 11*t + 1).
%t A168882 coxG[{21,66,-11}] (* The coxG program is at A169452 *) (* _Harvey P. Dale_, May 13 2019 *)
%Y A168882 Cf. A170732 (G.f.: (1+x)/(1-12*x)).
%K A168882 nonn
%O A168882 0,2
%A A168882 _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009