The number of length-n permutations avoiding the patterns 1234, 1324, 1432 and 3214.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =20a(5) =62a(6) =172a(7) =471a(8) =1337a(9) =3846a(10) =11030a(11) =31442a(12) =89470a(13) =254934a(14) =727203a(15) =2074435a(16) =5915652a(17) =16866988a(18) =48093810a(19) =137141828a(20) =391072846a(21) =1115164897a(22) =3179915535a(23) =9067592160a(24) =25856510664a(25) =73730732368a(26) =210245631360a(27) =599521974384