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 A168682 #19 Feb 22 2021 09:18:19
%S A168682 1,5,20,80,320,1280,5120,20480,81920,327680,1310720,5242880,20971520,
%T A168682 83886080,335544320,1342177280,5368709120,21474836470,85899345840,
%U A168682 343597383210,1374389532240,5497558126560,21990232496640,87960929948160
%N A168682 Number of reduced words of length n in Coxeter group on 5 generators S_i with relations (S_i)^2 = (S_i S_j)^17 = I.
%C A168682 The initial terms coincide with those of A003947, although the two sequences are eventually different.
%C A168682 First disagreement at index 17: a(17) = 21474836470, A003947(17) = 21474836480. - _Klaus Brockhaus_, Mar 30 2011
%C A168682 Computed with MAGMA using commands similar to those used to compute A154638.
%H A168682 G. C. Greubel, <a href="/A168682/b168682.txt">Table of n, a(n) for n = 0..500</a>
%H A168682 <a href="/index/Rec#order_17">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,-6).
%F A168682 G.f.: (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^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).
%F A168682 G.f.: (1+t)*(1-t^17)/(1 -4*t +9*t^17 -6*t^18). - _G. C. Greubel_, Feb 22 2021
%t A168682 CoefficientList[Series[(1+t)*(1-t^17)/(1 -4*t +9*t^17 -6*t^18), {t, 0, 40}], t] (* _G. C. Greubel_, Aug 03 2016, Feb 22 2021 *)
%t A168682 coxG[{17, 6, -3, 40}] (* The coxG program is at A169452 *) (* _G. C. Greubel_, Feb 22 2021 *)
%o A168682 (PARI) Vec(Pol(vector(18,i,if(i<2||i>17,1,2))) / Pol(vector(18,i,if(i<2,6,i>17,1,-3)))+O(x^99)) \\ _Charles R Greathouse IV_, Aug 03 2016
%o A168682 (Magma)
%o A168682 R<t>:=PowerSeriesRing(Integers(), 40);
%o A168682 Coefficients(R!( (1+t)*(1-t^17)/(1 -4*t +9*t^17 -6*t^18) )); // _G. C. Greubel_, Feb 22 2021
%o A168682 (Sage)
%o A168682 def A168682_list(prec):
%o A168682 P.<t> = PowerSeriesRing(ZZ, prec)
%o A168682 return P( (1+t)*(1-t^17)/(1 -4*t +9*t^17 -6*t^18) ).list()
%o A168682 A168682_list(40) # _G. C. Greubel_, Feb 22 2021
%Y A168682 Cf. A003947 (G.f.: (1+x)/(1-4*x)).
%K A168682 nonn,easy
%O A168682 0,2
%A A168682 _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009