A161977 Number of reduced words of length n in the Weyl group B_31.

1, 31, 495, 5425, 45879, 319145, 1900920, 9965384, 46909324, 201295028, 796809245, 2937251395, 10161553364, 33205476524, 103050077489, 305131440111, 865481871426, 2359754902590, 6203436293890, 15765840836350, 38828731002622

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..20.

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: A042866 A110824 A161636 * A162378 A162737 A010983

Adjacent sequences: A161974 A161975 A161976 * A161978 A161979 A161980

Keyword

nonn

Author

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

Status

approved