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 A167881 #16 Dec 07 2024 01:59:11
%S A167881 1,3,6,12,24,48,96,192,384,768,1536,3072,6144,12288,24576,49152,98301,
%T A167881 196596,393183,786348,1572660,3145248,6290352,12580416,25160256,
%U A167881 50319360,100636416,201268224,402527232,805036032,1610035200,3219996672
%N A167881 Number of reduced words of length n in Coxeter group on 3 generators S_i with relations (S_i)^2 = (S_i S_j)^16 = I.
%C A167881 The initial terms coincide with those of A003945, although the two sequences are eventually different.
%C A167881 Computed with MAGMA using commands similar to those used to compute A154638.
%H A167881 G. C. Greubel, <a href="/A167881/b167881.txt">Table of n, a(n) for n = 0..500</a>
%H A167881 <a href="/index/Rec#order_16">Index entries for linear recurrences with constant coefficients</a>, signature (1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,-1).
%F A167881 G.f.: (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)/(t^16 - t^15 - t^14 - t^13 - t^12 - t^11 - t^10 - t^9 - t^8 - t^7 - t^6 - t^5 - t^4 - t^3 - t^2 - t + 1).
%F A167881 From _G. C. Greubel_, Dec 06 2024: (Start)
%F A167881 a(n) = Sum_{j=1..15} a(n-j) - a(n-16).
%F A167881 G.f.: (1+x)*(1-x^16)/(1 - 2*x + 2*x^16 - x^17). (End)
%t A167881 CoefficientList[Series[(1+x)*(1-x^16)/(1-2*x+2*x^16-x^17), {x,0,50}], x] (* _G. C. Greubel_, Jun 29 2016; Dec 06 2024 *)
%t A167881 coxG[{16,1,-1}] (* The coxG program is at A169452 *) (* _G. C. Greubel_, Dec 06 2024 *)
%o A167881 (Magma)
%o A167881 R<x>:=PowerSeriesRing(Integers(), 40); Coefficients(R!( (1+x)*(1-x^16)/(1-2*x+2*x^16-x^17) )); // _G. C. Greubel_, Dec 06 2024
%o A167881 (SageMath)
%o A167881 def A167881_list(prec):
%o A167881 P.<x> = PowerSeriesRing(ZZ, prec)
%o A167881 return P( (1+x)*(1-x^16)/(1-2*x+2*x^16-x^17) ).list()
%o A167881 print(A167881_list(40)) # _G. C. Greubel_, Dec 06 2024
%Y A167881 Cf. A003945, A154638, A169452.
%K A167881 nonn
%O A167881 0,2
%A A167881 _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009