Number of permutations of length n which avoid the patterns 213, 1234, 2431.

Terms

a(0) =1a(1) =2a(2) =5a(3) =12a(4) =26a(5) =55a(6) =113a(7) =227a(8) =449a(9) =877a(10) =1696a(11) =3254a(12) =6203a(13) =11762a(14) =22205a(15) =41766a(16) =78316a(17) =146467a(18) =273313a(19) =509041a(20) =946531a(21) =1757541a(22) =3259480a(23) =6038576a(24) =11176989a(25) =20671462a(26) =38204837a(27) =70567516a(28) =130275854a(29) =240394475