Number of permutations of length n which avoid the patterns 1234, 1324, 2431.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =75a(5) =258a(6) =842a(7) =2614a(8) =7787a(9) =22466a(10) =63273a(11) =175044a(12) =477897a(13) =1291997a(14) =3467411a(15) =9254394a(16) =24595834a(17) =65158141a(18) =172181087a(19) =454099591a(20) =1195773446a(21) =3144999057a(22) =8263735626a(23) =21697177681a(24) =56933687000a(25) =149323655848