Number of permutations of length n which avoid the patterns 2134, 3421, 4231.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =73a(5) =233a(6) =677a(7) =1819a(8) =4606a(9) =11171a(10) =26274a(11) =60471a(12) =137059a(13) =307245a(14) =683171a(15) =1509595a(16) =3319028a(17) =7266583a(18) =15850872a(19) =34462295a(20) =74700801a(21) =161470161a(22) =348116785a(23) =748673435a(24) =1606409882a(25) =3439322827a(26) =7348417246a(27) =15669920663a(28) =33353112015