A164330 Number of reduced words of length n in Coxeter group on 45 generators S_i with relations (S_i)^2 = (S_i S_j)^6 = I.

1, 45, 1980, 87120, 3833280, 168664320, 7421229090, 326534036400, 14367495685950, 632169725893200, 27815464230602400, 1223880262963776000, 53850724390367020710, 2369431557254469630780, 104254974618644628784170

Offset: 0

Author

John Cannon and N. J. A. Sloane, Dec 03 2009

Keywords

• nonn

Comments

The initial terms coincide with those of A170764, although the two sequences are eventually different.

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

Links

• G. C. Greubel, Table of n, a(n) for n = 0..600
• Index entries for linear recurrences with constant coefficients, signature (43, 43, 43, 43, 43, -946).

Programs

Magma

R:=PowerSeriesRing(Integers(), 20); Coefficients(R!( (1+x)*(1-x^6)/(1-44*x+989*x^6-946*x^7) )); // G. C. Greubel, Apr 25 2019

Mathematica

CoefficientList[Series[(1+x)*(1-x^6)/(1-44*x+989*x^6-946*x^7), {x,0,20}], x] (* G. C. Greubel, Sep 14 2017, modified Apr 25 2019 *)
coxG[{6, 946, -43}] (* The coxG program is at A169452 *) (* G. C. Greubel, Apr 25 2019 *)

PARI

my(x='x+O('x^20)); Vec((1+x)*(1-x^6)/(1-44*x+989*x^6-946*x^7)) \\ G. C. Greubel, Sep 14 2017, modified Apr 25 2019

Sage

((1+x)*(1-x^6)/(1-44*x+989*x^6-946*x^7)).series(x, 20).coefficients(x, sparse=False) # G. C. Greubel, Apr 25 2019

Formula

G.f.: (t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(946*t^6 - 43*t^5 - 43*t^4 - 43*t^3 - 43*t^2 - 43*t + 1).

G.f.: (1+x)*(1-x^6)/(1 -44*x +989*x^6 -946*x^7). - G. C. Greubel, Apr 25 2019

a(n) = -946*a(n-6) + 43*Sum_{k=1..5} a(n-k). - Wesley Ivan Hurt, May 06 2021