Number of permutations of [n] avoiding {1324, 2143, 3421}.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =21a(5) =71a(6) =218a(7) =610a(8) =1585a(9) =3895a(10) =9186a(11) =21022a(12) =47061a(13) =103663a(14) =225618a(15) =486626a(16) =1042305a(17) =2220303a(18) =4708714a(19) =9949294a(20) =20956661a(21) =44022231a(22) =92253162a(23) =192912386a(24) =402622961a(25) =838825351a(26) =1744789138a(27) =3623830750a(28) =7516137525a(29) =15569193055