A165329 - OEIS

A165329

Number of reduced words of length n in Coxeter group on 18 generators S_i with relations (S_i)^2 = (S_i S_j)^9 = I.

1, 18, 306, 5202, 88434, 1503378, 25557426, 434476242, 7386096114, 125563633785, 2134581771744, 36287890075584, 616894130535840, 10487200206374784, 178282403291884896, 3030800852281773888, 51523614426225577248

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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, 16, 16, 16, 16, 16, 16, -136).

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)/(136*t^9 - 16*t^8 - 16*t^7 - 16*t^6 - 16*t^5 - 16*t^4 - 16*t^3 -

16*t^2 - 16*t + 1)

CROSSREFS

Sequence in context: A163967 A164630 A164892 * A165880 A166412 A166599

Adjacent sequences: A165326 A165327 A165328 * A165330 A165331 A165332

KEYWORD

nonn

AUTHOR

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

STATUS

approved