A165185 Number of reduced words of length n in Coxeter group on 5 generators S_i with relations (S_i)^2 = (S_i S_j)^9 = I.

1, 5, 20, 80, 320, 1280, 5120, 20480, 81920, 327670, 1310640, 5242410, 20969040, 83873760, 335485440, 1341903360, 5367459840, 21469224960, 85874442330, 343487939580, 1373912440470, 5495492494980, 21981340930320, 87922847594880

Offset

0,2

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

Table of n, a(n) for n=0..23.

Index entries for linear recurrences with constant coefficients, signature (3, 3, 3, 3, 3, 3, 3, 3, -6).

Formula

G.f. (t^9 + 2*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^9 - 3*t^8 - 3*t^7 - 3*t^6 - 3*t^5 - 3*t^4 - 3*t^3 - 3*t^2 - 3*t

+ 1)

Crossrefs

Sequence in context: A163878 A164354 A164706 * A165757 A166331 A166495

Adjacent sequences: A165182 A165183 A165184 * A165186 A165187 A165188

Keyword

nonn

Author

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

Status

approved