A164781 Number of reduced words of length n in Coxeter group on 12 generators S_i with relations (S_i)^2 = (S_i S_j)^8 = I.

1, 12, 132, 1452, 15972, 175692, 1932612, 21258732, 233845986, 2572305120, 28295348400, 311248745280, 3423735239760, 37661077095840, 414271732097520, 4556987777548800, 50126851522277970, 551395212406754100

Offset

0,2

Comments

The initial terms coincide with those of A003954, 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..17.

Index entries for linear recurrences with constant coefficients, signature (10, 10, 10, 10, 10, 10, 10, -55).

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)/(55*t^8 - 10*t^7 - 10*t^6 - 10*t^5 - 10*t^4 - 10*t^3 - 10*t^2 - 10*t + 1).

Mathematica

coxG[{8, 55, -10}] (* The coxG program is at A169452 *) (* Harvey P. Dale, Oct 17 2015 *)

Crossrefs

Sequence in context: A163957 A063813 A164601 * A165266 A165807 A166372

Adjacent sequences: A164778 A164779 A164780 * A164782 A164783 A164784

Keyword

nonn

Author

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

Status

approved