A161651 Number of reduced words of length n in the Weyl group A_38.

1, 38, 740, 9841, 100490, 840009, 5984563, 37358751, 208504842, 1056449420, 4918107194, 21239722205, 85769361157, 325992594164, 1172714551785, 4011922874670, 13106108017275, 41030950420668, 123490172703472

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 I.)

Links

Table of n, a(n) for n=0..18.

Formula

G.f. for A_m is the polynomial Prod_{k=1..m}(1-x^(k+1))/(1-x). Only finitely many terms are nonzero. This is a row of the triangle in A008302.

Crossrefs

Sequence in context: A269010 A010954 A035714 * A162166 A162392 A010990

Adjacent sequences: A161648 A161649 A161650 * A161652 A161653 A161654

Keyword

nonn

Author

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

Status

approved