Number of permutations of [n] avoiding {2143, 3412, 1234}.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =21a(5) =69a(6) =194a(7) =470a(8) =1009a(9) =1969a(10) =3562a(11) =6062a(12) =9813a(13) =15237a(14) =22842a(15) =33230a(16) =47105a(17) =65281a(18) =88690a(19) =118390a(20) =155573a(21) =201573a(22) =257874a(23) =326118a(24) =408113a(25) =505841a(26) =621466a(27) =757342a(28) =916021a(29) =1100261