A161879 Number of reduced words of length n in the Weyl group B_19.

1, 19, 189, 1311, 7124, 32300, 127091, 445721, 1420364, 4172476, 11426240, 29429784, 71808030, 166970290, 371826581, 796341623, 1646167391, 3294638285, 6401307860, 12102626404, 22312161586, 40184022430, 70815181390

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..22.

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: A193575 A161512 A162347 * A176600 A139619 A121039

Adjacent sequences: A161876 A161877 A161878 * A161880 A161881 A161882

Keyword

nonn

Author

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

Status

approved