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

Offset: 0

Author

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

Keywords

• nonn

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

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

Programs

Mathematica

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

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)