A162949 - OEIS

A162949

Number of reduced words of length n in Coxeter group on 8 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I.

1, 8, 56, 392, 2716, 18816, 130368, 903168, 6257076, 43348536, 300314952, 2080556856, 14413923468, 99858452400, 691810982352, 4792808455344, 33204174947748, 230035738812264, 1593668302662744, 11040800320974312

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OFFSET

0,2

COMMENTS

The initial terms coincide with those of A003950, although the two sequences are eventually different.

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

LINKS

Table of n, a(n) for n=0..19.

Index entries for linear recurrences with constant coefficients, signature (6, 6, 6, -21).

FORMULA

G.f.: (t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(21*t^4 - 6*t^3 - 6*t^2 - 6*t + 1)

MATHEMATICA

coxG[{4, 21, -6}] (* The coxG program is at A169452 *) (* Harvey P. Dale, May 04 2018 *)

CROSSREFS

Sequence in context: A214942 A010556 A010575 * A063812 A234274 A163347

Adjacent sequences: A162946 A162947 A162948 * A162950 A162951 A162952

KEYWORD

nonn

AUTHOR

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

STATUS

approved