A162804 Number of reduced words of length n in Coxeter group on 18 generators S_i with relations (S_i)^2 = (S_i S_j)^3 = I.

1, 18, 306, 5049, 83232, 1370880, 22579128, 371880576, 6124915584, 100877977152, 1661470525440, 27364587522048, 450697523867136, 7423033790767104, 122258117131149312, 2013603551504732160, 33164254102629777408

Offset

0,2

Comments

The initial terms coincide with those of A170737, 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..16.

Index entries for linear recurrences with constant coefficients, signature (16, 16, -136).

Formula

G.f.: (t^3 + 2*t^2 + 2*t + 1)/(136*t^3 - 16*t^2 - 16*t + 1)

Crossrefs

Sequence in context: A161599 A273434 A083451 * A097831 A342885 A163104

Adjacent sequences: A162801 A162802 A162803 * A162805 A162806 A162807

Keyword

nonn

Author

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

Status

approved