Number of permutations of length n which avoid the patterns 1342, 3421, 4213.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =73a(5) =244a(6) =787a(7) =2468a(8) =7570a(9) =22809a(10) =67727a(11) =198664a(12) =576775a(13) =1659914a(14) =4741254a(15) =13454541a(16) =37964341a(17) =106590076a(18) =297951451a(19) =829614896a(20) =2301930586a(21) =6367200417a(22) =17562228251a(23) =48317182096a(24) =132621950863a(25) =363253065494