Number of permutations of length n which avoid the patterns 1234, 3142, 3421.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =71a(5) =208a(6) =526a(7) =1174a(8) =2370a(9) =4416a(10) =7714a(11) =12783a(12) =20277a(13) =31004a(14) =45946a(15) =66280a(16) =93400a(17) =128940a(18) =174798a(19) =233161a(20) =306531a(21) =397752a(22) =510038a(23) =647002a(24) =812686a(25) =1011592a(26) =1248714a(27) =1529571a(28) =1860241a(29) =2247396