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A161900 Number of reduced words of length n in the Weyl group B_22. 0
1, 22, 252, 2002, 12396, 63734, 283107, 1116236, 3983485, 13057330, 39764011, 113533312, 306173263, 784654154, 1920802566, 4510960122, 10201294213, 22286443124, 47167714715, 96947735390, 193938666735, 378324531180 (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 II.)

LINKS

Table of n, a(n) for n=0..21.

FORMULA

G.f. for B_m is the polynomial Prod_{k=1..m}(1-x^(2k))/(1-x). Only finitely many terms are nonzero. This is a row of the triangle in A128084.

CROSSREFS

Sequence in context: A109251 A268791 A161521 * A162364 A028571 A162679

Adjacent sequences:  A161897 A161898 A161899 * A161901 A161902 A161903

KEYWORD

nonn

AUTHOR

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

STATUS

approved

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Last modified July 26 17:37 EDT 2021. Contains 346294 sequences. (Running on oeis4.)