%I #5 Jul 19 2015 10:33:26
%S 1,20,209,1519,8624,40734,166495,604902,1991637,6029727,16976806,
%T 44853151,112016669,266039599,603919164,1315952428,2762629983,
%U 5605337934,11022366544,21056764914,39163212165,71048746505
%N Number of reduced words of length n in the Weyl group A_20.
%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
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