A163219 Number of reduced words of length n in Coxeter group on 36 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I.

1, 36, 1260, 44100, 1542870, 53978400, 1888472880, 66069561600, 2311490430270, 80869130653500, 2829263840578980, 98983800307381500, 3463018394666864670, 121156152466965222600, 4238733846520797445080, 148295107229819712107400

Offset

0,2

Comments

The initial terms coincide with those of A170755, 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..645

Index entries for linear recurrences with constant coefficients, signature (34, 34, 34, -595).

Formula

G.f.: (t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(595*t^4 - 34*t^3 - 34*t^2 - 34*t + 1).

a(n) = -595*a(n-4) + 34*Sum_{k=1..3} a(n-k). - Wesley Ivan Hurt, May 05 2021

Mathematica

CoefficientList[Series[(t^4+2*t^3+2*t^2+2*t+1)/(595*t^4-34*t^3-34*t^2 - 34*t+1), {t, 0, 20}], t] (* or *) Join[{1}, LinearRecurrence[{34, 34, 34, -595}, {36, 1260, 44100, 1542870}, 20]] (* G. C. Greubel, Dec 11 2016 *)
coxG[{4, 595, -34}] (* The coxG program is at A169452 *) (* G. C. Greubel, Apr 30 2019 *)

Prog

(PARI) my(t='t+O('t^20)); Vec((t^4+2*t^3+2*t^2+2*t+1)/(595*t^4-34*t^3 - 34*t^2-34*t+1)) \\ G. C. Greubel, Dec 11 2016
(Magma) R<x>:=PowerSeriesRing(Integers(), 20); Coefficients(R!( (1+x)*(1-x^4)/(1-35*x+629*x^4-595*x^5) )); // G. C. Greubel, Apr 30 2019
(SageMath) ((1+x)*(1-x^4)/(1-35*x+629*x^4-595*x^5)).series(x, 20).coefficients(x, sparse=False) # G. C. Greubel, Apr 30 2019

Crossrefs

Cf. A154638, A170755.

Sequence in context: A060786 A270961 A162850 * A163601 A164069 A164672

Adjacent sequences: A163216 A163217 A163218 * A163220 A163221 A163222

Keyword

nonn,easy

Author

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

Status

approved