Number of reduced words of length n in the Weyl group B_21.

Terms

a(0) =1a(1) =21a(2) =230a(3) =1750a(4) =10394a(5) =51338a(6) =219373a(7) =833129a(8) =2867249a(9) =9073845a(10) =26706681a(11) =73769301a(12) =192639951a(13) =478480891a(14) =1136148412a(15) =2590157556a(16) =5690334091a(17) =12085148911a(18) =24881271591a(19) =49780020675a(20) =96990931345a(21) =184385864445a(22) =342595978935a(23) =623097898035