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A161521
Number of reduced words of length n in the Weyl group A_22.
0
1, 22, 252, 2001, 12374, 63481, 281083, 1103587, 3917728, 12761596, 38582270, 109256095, 291946589, 740676682, 1793325939, 4161927624, 9293159292, 20029728894, 41788665040, 84604366100, 166583279325, 319610939055
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: A252819 A109251 A268791 * A161900 A162364 A028571
KEYWORD
nonn
AUTHOR
John Cannon and N. J. A. Sloane, Nov 30 2009
STATUS
approved