Number of reduced words of length n in the Weyl group A_20.

Terms

a(0) =1a(1) =20a(2) =209a(3) =1519a(4) =8624a(5) =40734a(6) =166495a(7) =604902a(8) =1991637a(9) =6029727a(10) =16976806a(11) =44853151a(12) =112016669a(13) =266039599a(14) =603919164a(15) =1315952428a(16) =2762629983a(17) =5605337934a(18) =11022366544a(19) =21056764914a(20) =39163212165a(21) =71048746505a(22) =125938520207a(23) =218444465922a(24) =371273650166a(25) =619085883331