A161878 - OEIS

%I #5 Jul 19 2015 10:26:04

%S 1,18,170,1122,5813,25176,94791,318630,974643,2752112,7253764,

%T 18003544,42378246,95162260,204856291,424515042,849825768,1648470894,

%U 3106669575,5701318544,10209535182,17871860844,30631158960,51476623220,84931612739

%N Number of reduced words of length n in the Weyl group B_18.

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

%D J. E. Humphreys, Reflection Groups and Coxeter Groups, Cambridge, 1990. See under Poincaré polynomial.

%D N. Bourbaki, Groupes et alg. de Lie, Chap. 4, 5, 6. (The group is defined in Planche II.)

%F 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.

%K nonn

%O 0,2

%A _John Cannon_ and _N. J. A. Sloane_, Nov 30 2009