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

Terms

a(0) =1a(1) =2a(2) =6a(3) =22a(4) =86a(5) =338a(6) =1318a(7) =5106a(8) =19718a(9) =76066a(10) =293398a(11) =1131794a(12) =4366374a(13) =16846018a(14) =64995254a(15) =250765298a(16) =967503814a(17) =3732821922a(18) =14401956182a(19) =55565542354a(20) =214382633062a(21) =827129764994