Number of permutations of length n which avoid the patterns 2134, 3421, 4123.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =71a(5) =209a(6) =533a(7) =1205a(8) =2473a(9) =4696a(10) =8372a(11) =14169a(12) =22959a(13) =35855a(14) =54251a(15) =79865a(16) =114785a(17) =161518a(18) =223042a(19) =302861a(20) =405063a(21) =534381a(22) =696257a(23) =896909a(24) =1143401a(25) =1443716a(26) =1806832a(27) =2242801a(28) =2762831a(29) =3379371