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A161518 Number of reduced words of length n in the Weyl group A_21. 0
1, 21, 230, 1749, 10373, 51107, 217602, 822504, 2814141, 8843868, 25820674, 70673825, 182690494, 448730093, 1052649257, 2368601685, 5131231668, 10736569602, 21758936146, 42815701060, 81978913225, 153027659730 (list; graph; refs; listen; history; text; internal format)
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
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: A027508 A221037 A221500 * A162360 A161899 A220721
KEYWORD
nonn
AUTHOR
John Cannon and N. J. A. Sloane, Nov 30 2009
STATUS
approved

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Last modified April 17 01:50 EDT 2024. Contains 371756 sequences. (Running on oeis4.)