

A161571


Number of reduced words of length n in the Weyl group A_28.


0



1, 28, 405, 4031, 31030, 196882, 1071637, 5142716, 22195440, 87455155, 318311627, 1080299532, 3445025535, 10388772051, 29784426945, 81555340856, 214122343813, 540880490745, 1318464472031, 3109618390150, 7112648815656, 15810488782208
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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 PoincarĂ© 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..21.


FORMULA

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


CROSSREFS

Sequence in context: A297179 A269255 A125463 * A161956 A162370 A162727
Adjacent sequences: A161568 A161569 A161570 * A161572 A161573 A161574


KEYWORD

nonn


AUTHOR

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


STATUS

approved



