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 A168880 #10 Nov 25 2016 09:34:00
%S A168880 1,11,110,1100,11000,110000,1100000,11000000,110000000,1100000000,
%T A168880 11000000000,110000000000,1100000000000,11000000000000,
%U A168880 110000000000000,1100000000000000,11000000000000000,110000000000000000
%N A168880 Number of reduced words of length n in Coxeter group on 11 generators S_i with relations (S_i)^2 = (S_i S_j)^21 = I.
%C A168880 The initial terms coincide with those of A003953, although the two sequences are eventually different.
%C A168880 First disagreement at index 21: a(21) = 1099999999999999999945, A003953(21) = 1100000000000000000000. - Klaus Brockhaus, Apr 05 2011
%C A168880 Computed with MAGMA using commands similar to those used to compute A154638.
%H A168880 <a href="/index/Rec#order_21">Index entries for linear recurrences with constant coefficients</a>, signature (9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, -45).
%F A168880 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)/(45*t^21 - 9*t^20 - 9*t^19 - 9*t^18 - 9*t^17 - 9*t^16 - 9*t^15 - 9*t^14 - 9*t^13 - 9*t^12 - 9*t^11 - 9*t^10 - 9*t^9 - 9*t^8 - 9*t^7 - 9*t^6 - 9*t^5 - 9*t^4 - 9*t^3 - 9*t^2 - 9*t + 1).
%t A168880 With[{num=Total[2t^Range[20]]+t^21+1,den=Total[-9 t^Range[20]]+ 45t^21+ 1},CoefficientList[Series[num/den,{t,0,30}],t]] (* _Harvey P. Dale_, Feb 19 2013 *)
%Y A168880 Cf. A003953 (G.f.: (1+x)/(1-10*x)).
%K A168880 nonn
%O A168880 0,2
%A A168880 _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009