

A162402


Number of reduced words of length n in the Weyl group D_40.


0



1, 40, 819, 11440, 122589, 1074488, 8020830, 52427192, 306189025, 1622495952, 7895219982, 35623107520, 150221110689, 595982725640, 2237008815175, 7981961442768, 27186526166255, 88708246063240, 278172606877930
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OFFSET

0,2


COMMENTS

Computed with MAGMA using commands similar to those used to compute A161409.


REFERENCES

N. Bourbaki, Groupes et alg. de Lie, Chap. 4, 5, 6. (The group is defined in Planche IV.)
J. E. Humphreys, Reflection Groups and Coxeter Groups, Cambridge, 1990. See under PoincarĂ© polynomial.


LINKS

Table of n, a(n) for n=0..18.


FORMULA

G.f. for D_m is the polynomial f(n) * Product( f(2i), i=1..n1 )/ f(1)^n, where f(k) = 1x^k. Only finitely many terms are nonzero. This is a row of the triangle in A162206.


CROSSREFS

Sequence in context: A035609 A161653 A162176 * A010992 A250584 A004421
Adjacent sequences: A162399 A162400 A162401 * A162403 A162404 A162405


KEYWORD

nonn


AUTHOR

John Cannon and N. J. A. Sloane, Dec 01 2009


STATUS

approved



