

A161512


Number of reduced words of length n in the Weyl group A_19.


0



1, 19, 189, 1310, 7105, 32110, 125761, 438407, 1386735, 4038090, 10947079, 27876345, 67163518, 154022930, 337879565, 712033264, 1446677555, 2842707951, 5417028610, 10034398370, 18106447251, 31885534341, 54889773721, 92505945904
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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 PoincarĂ© polynomial.
N. Bourbaki, Groupes et alg. de Lie, Chap. 4, 5, 6. (The group is defined in Planche I.)


LINKS

Table of n, a(n) for n=0..23.


FORMULA

G.f. for A_m is the polynomial Prod_{k=1..m}(1x^(k+1))/(1x). Only finitely many terms are nonzero. This is a row of the triangle in A008302.


CROSSREFS

Sequence in context: A327848 A034273 A193575 * A162347 A161879 A176600
Adjacent sequences: A161509 A161510 A161511 * A161513 A161514 A161515


KEYWORD

nonn


AUTHOR

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


STATUS

approved



