A162960 Number of reduced words of length n in Coxeter group on 9 generators S_i with relations (S_i)^2 = (S_i S_j)^4 = I.

1, 9, 72, 576, 4572, 36288, 288036, 2286144, 18145260, 144020016, 1143094932, 9072809424, 72011403324, 571558593312, 4536492984324, 36006402202848, 285784857170316, 2268290625889680, 18003551393278836, 142895208872692080

Offset: 0

Author

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

Keywords

• nonn

Comments

The initial terms coincide with those of A003951, 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 (7, 7, 7, -28).

Formula

G.f.: (t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(28*t^4 - 7*t^3 - 7*t^2 - 7*t + 1)