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Number of reduced words of length n in Coxeter group on 32 generators S_i with relations (S_i)^2 = (S_i S_j)^16 = I.
7

%I #21 Sep 07 2023 18:19:44

%S 1,32,992,30752,953312,29552672,916132832,28400117792,880403651552,

%T 27292513198112,846067909141472,26228105183385632,813071260684954592,

%U 25205209081233592352,781361481518241362912,24222205927065482250272

%N Number of reduced words of length n in Coxeter group on 32 generators S_i with relations (S_i)^2 = (S_i S_j)^16 = I.

%C The initial terms coincide with those of A170751, although the two sequences are eventually different.

%C Computed with MAGMA using commands similar to those used to compute A154638.

%H G. C. Greubel, <a href="/A167947/b167947.txt">Table of n, a(n) for n = 0..500</a>

%H <a href="/index/Rec#order_16">Index entries for linear recurrences with constant coefficients</a>, signature (30,30,30,30,30,30,30,30,30,30,30,30,30,30,30,-465).

%F 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)/( 465*t^16 - 30*t^15 - 30*t^14 - 30*t^13 - 30*t^12 - 30*t^11 - 30*t^10 - 30*t^9 - 30*t^8 - 30*t^7 - 30*t^6 - 30*t^5 - 30*t^4 - 30*t^3 - 30*t^2 - 30*t + 1).

%F From _G. C. Greubel_, Sep 07 2023: (Start)

%F G.f.: (1+t)*(1-t^16)/(1 - 31*t + 495*t^16 - 465*t^17).

%F a(n) = 30*Sum_{j=1..15} a(n-j) - 465*a(n-16). (End)

%t coxG[{16,465,-30}] (* The coxG program is at A169452 *) (* _Harvey P. Dale_, Apr 16 2015 *)

%t CoefficientList[Series[(1+t)*(1-t^16)/(1-31*t+495*t^16-465*t^17), {t, 0, 50}], t] (* _G. C. Greubel_, Jul 02 2016; Sep 07 2023 *)

%o (Magma) R<x>:=PowerSeriesRing(Integers(), 40); Coefficients(R!( (1+x)*(1-x^16)/(1-31*x+495*x^16-465*x^17) )); // _G. C. Greubel_, Sep 07 2023

%o (SageMath)

%o def A167947_list(prec):

%o P.<x> = PowerSeriesRing(ZZ, prec)

%o return P( (1+x)*(1-x^16)/(1-31*x+495*x^16-465*x^17) ).list()

%o A167947_list(40) # _G. C. Greubel_, Sep 07 2023

%Y Cf. A154638, A169452, A170751.

%K nonn

%O 0,2

%A _John Cannon_ and _N. J. A. Sloane_, Dec 03 2009