Number of permutations of [n] avoiding {1243, 2431, 3412}.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =21a(5) =73a(6) =240a(7) =748a(8) =2240a(9) =6525a(10) =18653a(11) =52640a(12) =147210a(13) =408957a(14) =1130398a(15) =3112172a(16) =8540753a(17) =23375439a(18) =63830072a(19) =173949534a(20) =473211976a(21) =1285299971a(22) =3486071977a(23) =9442928926a(24) =25548319586a(25) =69046732343a(26) =186416183910a(27) =502821645418