A164706 Number of reduced words of length n in Coxeter group on 5 generators S_i with relations (S_i)^2 = (S_i S_j)^8 = I.

1, 5, 20, 80, 320, 1280, 5120, 20480, 81910, 327600, 1310250, 5240400, 20959200, 83827200, 335270400, 1340928000, 5363097690, 21449933820, 85789908630, 343120332420, 1372324139280, 5488667867520, 21952156999680, 87798571269120

Offset: 0

Author

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

Keywords

• nonn

Comments

The initial terms coincide with those of A003947, 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 (3, 3, 3, 3, 3, 3, 3, -6).

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