A161512 Number of reduced words of length n in the Weyl group A_19.

1, 19, 189, 1310, 7105, 32110, 125761, 438407, 1386735, 4038090, 10947079, 27876345, 67163518, 154022930, 337879565, 712033264, 1446677555, 2842707951, 5417028610, 10034398370, 18106447251, 31885534341, 54889773721, 92505945904

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

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

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: 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