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 A165939 #15 Sep 08 2022 08:45:48
%S A165939 1,23,506,11132,244904,5387888,118533536,2607737792,57370231424,
%T A165939 1262145091328,27767192008963,610878224191620,13439320932093441,
%U A165939 295665060503367324,6504631331014936812,143101889281027434912
%N A165939 Number of reduced words of length n in Coxeter group on 23 generators S_i with relations (S_i)^2 = (S_i S_j)^10 = I.
%C A165939 The initial terms coincide with those of A170742, although the two sequences are eventually different.
%C A165939 Computed with MAGMA using commands similar to those used to compute A154638.
%H A165939 G. C. Greubel, <a href="/A165939/b165939.txt">Table of n, a(n) for n = 0..500</a>
%H A165939 <a href="/index/Rec#order_10">Index entries for linear recurrences with constant coefficients</a>, signature (21,21,21,21,21,21,21,21,21,-231).
%F A165939 G.f.: (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)/(231*t^10 - 21*t^9 - 21*t^8 - 21*t^7 - 21*t^6 - 21*t^5 - 21*t^4 - 21*t^3 - 21*t^2 - 21*t + 1).
%p A165939 seq(coeff(series((1+t)*(1-t^10)/(1-22*t+252*t^10-231*t^11), t, n+1), t, n), n = 0..30); # _G. C. Greubel_, Sep 25 2019
%t A165939 CoefficientList[Series[(1+t)*(1-t^10)/(1-22*t+252*t^10-231*t^11), {t, 0, 25}], t] (* _G. C. Greubel_, Apr 18 2016 *)
%t A165939 coxG[{10, 231, -21}] (* The coxG program is at A169452 *) (* _G. C. Greubel_, Sep 25 2019 *)
%o A165939 (PARI) my(t='t+O('t^30)); Vec((1+t)*(1-t^10)/(1-22*t+252*t^10-231*t^11)) \\ _G. C. Greubel_, Sep 25 2019
%o A165939 (Magma) R<t>:=PowerSeriesRing(Integers(), 30); Coefficients(R!( (1+t)*(1-t^10)/(1-22*t+252*t^10-231*t^11) )); // _G. C. Greubel_, Sep 25 2019
%o A165939 (Sage)
%o A165939 def A165939_list(prec):
%o A165939 P.<t> = PowerSeriesRing(ZZ, prec)
%o A165939 return P((1+t)*(1-t^10)/(1-22*t+252*t^10-231*t^11)).list()
%o A165939 A165939_list(30) # _G. C. Greubel_, Sep 25 2019
%o A165939 (GAP) a:=[23, 506, 11132, 244904, 5387888, 118533536, 2607737792, 57370231424, 1262145091328, 27767192008963];; for n in [11..30] do a[n]:=21*Sum([1..9], j-> a[n-j]) -231*a[n-10]; od; Concatenation([1], a); # _G. C. Greubel_, Sep 25 2019
%K A165939 nonn
%O A165939 0,2
%A A165939 _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009