A164909 - OEIS

A164909

Number of reduced words of length n in Coxeter group on 19 generators S_i with relations (S_i)^2 = (S_i S_j)^8 = I.

1, 19, 342, 6156, 110808, 1994544, 35901792, 646232256, 11632180437, 209379244788, 3768826350951, 67838873322924, 1221099701917140, 21979794312389664, 395636291824874544, 7121453148481232448

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OFFSET

0,2

COMMENTS

The initial terms coincide with those of A170738, 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..15.

Index entries for linear recurrences with constant coefficients, signature (17, 17, 17, 17, 17, 17, 17, -153).

FORMULA

G.f. (t^8 + 2*t^7 + 2*t^6 + 2*t^5 + 2*t^4 + 2*t^3 + 2*t^2 + 2*t + 1)/(153*t^8 -

17*t^7 - 17*t^6 - 17*t^5 - 17*t^4 - 17*t^3 - 17*t^2 - 17*t + 1)

CROSSREFS

Sequence in context: A163453 A163968 A164631 * A165341 A165881 A166413

Adjacent sequences: A164906 A164907 A164908 * A164910 A164911 A164912

KEYWORD

nonn

AUTHOR

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

STATUS

approved