Number of permutations of [n] avoiding {2143, 1432, 1324}.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =21a(5) =77a(6) =289a(7) =1103a(8) =4261a(9) =16603a(10) =65100a(11) =256466a(12) =1014107a(13) =4021836a(14) =15988827a(15) =63691619a(16) =254145940a(17) =1015570446a(18) =4063266013a(19) =16274491491a(20) =65245082548a(21) =261786577155