Number of permutations of length n which avoid the patterns 4321 and 3142.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =22a(5) =86a(6) =338a(7) =1314a(8) =5046a(9) =19190a(10) =72482a(11) =272530a(12) =1021734a(13) =3823622a(14) =14293234a(15) =53394370a(16) =199382550a(17) =744348822a(18) =2778471490a(19) =10370520178a(20) =38705706374a(21) =144456761766a(22) =539130777874