Number of permutations of [n] avoiding {4231, 2341, 4123}.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =21a(5) =75a(6) =259a(7) =862a(8) =2808a(9) =9090a(10) =29489a(11) =96076a(12) =314011a(13) =1027749a(14) =3364559a(15) =11012071a(16) =36033146a(17) =117891838a(18) =385711145a(19) =1261999184a(20) =4129291969a(21) =13511534900a(22) =44211907218a(23) =144668866862a(24) =473380823897