Dimensions of graded algebra associated with meanders.

Terms

a(0) =1a(1) =4a(2) =15a(3) =56a(4) =207a(5) =764a(6) =2805a(7) =10288a(8) =37609a(9) =137380a(10) =500655a(11) =1823440a(12) =6629423a(13) =24090332a(14) =87418221a(15) =317085352a(16) =1148825185a(17) =4160744164a(18) =15054719697a(19) =54454345624a(20) =196805925995a(21) =711077858188