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 A164664 #15 Sep 08 2022 08:45:47
%S A164664 1,28,756,20412,551124,14880348,401769396,10847773314,292889869272,
%T A164664 7908026195160,213516699839352,5764950695053368,155653663349994264,
%U A164664 4202648764205784984,113471512684966713186,3063730735882188973692
%N A164664 Number of reduced words of length n in Coxeter group on 28 generators S_i with relations (S_i)^2 = (S_i S_j)^7 = I.
%C A164664 The initial terms coincide with those of A170747, although the two sequences are eventually different.
%C A164664 Computed with MAGMA using commands similar to those used to compute A154638.
%H A164664 G. C. Greubel, <a href="/A164664/b164664.txt">Table of n, a(n) for n = 0..695</a>
%H A164664 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (26,26,26,26,26,26,-351).
%F A164664 G.f.: (t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(351*t^7 - 26*t^6 - 26*t^5 - 26*t^4 - 26*t^3 - 26*t^2 - 26*t + 1).
%p A164664 seq(coeff(series((1+t)*(1-t^7)/(1-27*t+377*t^7-351*t^8), t, n+1), t, n), n = 0 .. 30); # _G. C. Greubel_, Sep 15 2019
%t A164664 CoefficientList[Series[(t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(351*t^7 - 26*t^6 - 26*t^5 - 26*t^4 - 26*t^3 - 26*t^2 - 26*t + 1), {t, 0, 20}], t] (* _Wesley Ivan Hurt_, Apr 25 2017 *)
%t A164664 coxG[{7,351,-26}] (* The coxG program is at A169452 *) (* _Harvey P. Dale_, Aug 13 2018 *)
%o A164664 (PARI) my(t='t+O('t^20)); Vec((1+t)*(1-t^7)/(1-27*t+377*t^7-351*t^8)) \\ _G. C. Greubel_, Sep 15 2019
%o A164664 (Magma) R<t>:=PowerSeriesRing(Integers(), 20); Coefficients(R!( (1+t)*(1-t^7)/(1-27*t+377*t^7-351*t^8) )); // _G. C. Greubel_, Sep 15 2019
%o A164664 (Sage)
%o A164664 def A164664_list(prec):
%o A164664 P.<t> = PowerSeriesRing(ZZ, prec)
%o A164664 return P((1+t)*(1-t^7)/(1-27*t+377*t^7-351*t^8)).list()
%o A164664 A164664_list(20) # _G. C. Greubel_, Sep 15 2019
%o A164664 (GAP) a:=[28,756,20412,551124,14880348,401769396,10847773314];; for n in [8..30] do a[n]:=26*(a[n-1] +a[n-2]+a[n-3]+a[n-4]+a[n-5]+a[n-6]) -351*a[n-7]; od; Concatenation([1], a); # _G. C. Greubel_, Sep 15 2019
%Y A164664 Cf. A154638, A170747.
%K A164664 nonn
%O A164664 0,2
%A A164664 _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009