Number of permutations of [n] avoiding {1342, 2143, 3412}.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =21a(5) =73a(6) =244a(7) =790a(8) =2505a(9) =7839a(10) =24320a(11) =74998a(12) =230243a(13) =704359a(14) =2148620a(15) =6538740a(16) =19859175a(17) =60213343a(18) =182304334a(19) =551269876a(20) =1665215691a(21) =5025508101a(22) =15154701002a(23) =45668771716a(24) =137542144181a(25) =414029250493