Number of permutations of length n which avoid the patterns 2134, 3241, 3421.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =75a(5) =255a(6) =813a(7) =2443a(8) =6985a(9) =19175a(10) =50917a(11) =131555a(12) =332257a(13) =823263a(14) =2007005a(15) =4825051a(16) =11460569a(17) =26935255a(18) =62717909a(19) =144834515a(20) =332005329a(21) =756023247a(22) =1711275981a(23) =3852468171a(24) =8629780425a(25) =19243466695a(26) =42731569093a(27) =94522834883