A161512 - OEIS

%I #5 Jul 19 2015 10:33:36

%S 1,19,189,1310,7105,32110,125761,438407,1386735,4038090,10947079,

%T 27876345,67163518,154022930,337879565,712033264,1446677555,

%U 2842707951,5417028610,10034398370,18106447251,31885534341,54889773721,92505945904

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

%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 I.)

%F 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.

%K nonn

%O 0,2

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