Number of permutations of [n] avoiding {4231, 4123, 1234}.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =21a(5) =75a(6) =253a(7) =774a(8) =2130a(9) =5314a(10) =12169a(11) =25895a(12) =51756a(13) =98034a(14) =177282a(15) =307933a(16) =516327a(17) =839223a(18) =1326868a(19) =2046700a(20) =3087767a(21) =4565949a(22) =6630075a(23) =9469032a(24) =13319968a(25) =18477696a(26) =25305411a(27) =34246837a(28) =45839926a(29) =60732236