A161877 Number of reduced words of length n in the Weyl group B_17.

1, 17, 152, 952, 4691, 19363, 69615, 223839, 656013, 1777469, 4501652, 10749780, 24374702, 52784014, 109694031, 219658751, 425310726, 798645126, 1458198681, 2594648969, 4508216638, 7662325662, 12759298116, 20845464260, 33454989519

Offset

0,2

Comments

Computed with MAGMA using commands similar to those used to compute A161409.

References

J. E. Humphreys, Reflection Groups and Coxeter Groups, Cambridge, 1990. See under Poincaré polynomial.

N. Bourbaki, Groupes et alg. de Lie, Chap. 4, 5, 6. (The group is defined in Planche II.)

Links

Table of n, a(n) for n=0..24.

Formula

G.f. for B_m is the polynomial Prod_{k=1..m}(1-x^(2k))/(1-x). Only finitely many terms are nonzero. This is a row of the triangle in A128084.

Crossrefs

Sequence in context: A064102 A161497 A162328 * A221737 A139617 A188353

Adjacent sequences: A161874 A161875 A161876 * A161878 A161879 A161880

Keyword

nonn

Author

John Cannon and N. J. A. Sloane, Nov 30 2009

Status

approved