A162178 Number of reduced words of length n in the Weyl group B_41.

1, 41, 860, 12300, 134889, 1209377, 9230207, 61657399, 367846424, 1990342376, 9885562358, 45508669878, 195729780567, 791712506207, 3028721321382, 11010682764150, 38197208930405, 126905454993645, 405078061871575

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..18.

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: A346981 A299332 A161662 * A162403 A010993 A208431

Adjacent sequences: A162175 A162176 A162177 * A162179 A162180 A162181

Keyword

nonn

Author

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

Status

approved