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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
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.)
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: A297179 A269255 A125463 * A161956 A162370 A162727
KEYWORD
nonn
AUTHOR
John Cannon and N. J. A. Sloane, Nov 30 2009
STATUS
approved