Number of reduced words of length n in the Weyl group A_21.

Terms

a(0) =1a(1) =21a(2) =230a(3) =1749a(4) =10373a(5) =51107a(6) =217602a(7) =822504a(8) =2814141a(9) =8843868a(10) =25820674a(11) =70673825a(12) =182690494a(13) =448730093a(14) =1052649257a(15) =2368601685a(16) =5131231668a(17) =10736569602a(18) =21758936146a(19) =42815701060a(20) =81978913225a(21) =153027659730a(22) =278966179936a(23) =497410645838a(24) =868684295795