A162806 Number of reduced words of length n in Coxeter group on 20 generators S_i with relations (S_i)^2 = (S_i S_j)^3 = I.

1, 20, 380, 7030, 129960, 2400840, 44352270, 819332820, 15135787980, 279607936230, 5165281123560, 95419783331640, 1762718203098270, 32563220683609620, 601550117011031580, 11112615265773737430

Offset: 0

Author

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

Keywords

• nonn

Comments

The initial terms coincide with those of A170739, 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 (18, 18, -171).

Programs

Mathematica

coxG[{3,171,-18}] (* The coxG program is at A169452 *) (* Harvey P. Dale, Jul 10 2020 *)

Formula

G.f.: (t^3 + 2*t^2 + 2*t + 1)/(171*t^3 - 18*t^2 - 18*t + 1)