Number of permutations of length n which avoid the patterns 2134, 3421, 4132.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =71a(5) =213a(6) =564a(7) =1340a(8) =2909a(9) =5860a(10) =11090a(11) =19911a(12) =34179a(13) =56447a(14) =90144a(15) =139782a(16) =211193a(17) =311798a(18) =450910a(19) =640073a(20) =893439a(21) =1228185a(22) =1664972a(23) =2228448a(24) =2947797a(25) =3857336a(26) =4997162a(27) =6413851a(28) =8161211a(29) =10301091