A164332 Number of reduced words of length n in Coxeter group on 47 generators S_i with relations (S_i)^2 = (S_i S_j)^6 = I.

1, 47, 2162, 99452, 4574792, 210440432, 9680258791, 445291854660, 20483423028045, 942237354119580, 43342913451658140, 1993773796235517600, 91713584389960162440, 4218824411042032288125, 194065901246713684538250

Offset: 0

Author

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

Keywords

• nonn

Comments

The initial terms coincide with those of A170766, 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 (45, 45, 45, 45, 45, -1035).

Programs

Magma

R:=PowerSeriesRing(Integers(), 20); Coefficients(R!( (1+x)*(1-x^6)/(1-46*x+1080*x^6-1035*x^7) )); // G. C. Greubel, Apr 25 2019

Mathematica

CoefficientList[Series[(1+x)*(1-x^6)/(1-46*x+1080*x^6-1035*x^7), {x, 0, 20}], x] (* G. C. Greubel, Sep 14 2017, modified Apr 25 2019 *)
coxG[{6, 1035, -45}] (* 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)/(1-46*x+1080*x^6-1035*x^7)) \\ G. C. Greubel, Sep 14 2017, modified Apr 25 2019

Sage

((1+x)*(1-x^6)/(1-46*x+1080*x^6-1035*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)/(1035*t^6 - 45*t^5 - 45*t^4 - 45*t^3 - 45*t^2 - 45*t + 1).

G.f.: (1+x)*(1-x^6)/(1 -46*x +1080*x^6 -1035*x^7). - G. C. Greubel, Apr 25 2019

a(n) = -1035*a(n-6) + 45*Sum_{k=1..5} a(n-k). - Wesley Ivan Hurt, May 06 2021