A164769 Number of reduced words of length n in Coxeter group on 8 generators S_i with relations (S_i)^2 = (S_i S_j)^8 = I.

1, 8, 56, 392, 2744, 19208, 134456, 941192, 6588316, 46118016, 322824768, 2259763968, 15818281920, 110727512448, 775089360192, 5425602932736, 37979062409652, 265852330035768, 1860958562459976, 13026655702912824

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, 6, 6, 6, 6, -21).

Formula

G.f.: (t^8 + 2*t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(21*t^8 - 6*t^7 - 6*t^6 - 6*t^5 - 6*t^4 - 6*t^3 - 6*t^2 - 6*t + 1).

Crossrefs

Sequence in context: A163347 A163924 A164373 * A165215 A165786 A166366

Adjacent sequences: A164766 A164767 A164768 * A164770 A164771 A164772

Keyword

nonn

Author

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

Status

approved