Number of permutations of length n which avoid the patterns 1234, 3421, 4231.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =73a(5) =228a(6) =616a(7) =1460a(8) =3110a(9) =6082a(10) =11102a(11) =19155a(12) =31539a(13) =49924a(14) =76416a(15) =113626a(16) =164744a(17) =233618a(18) =324838a(19) =443825a(20) =596925a(21) =791508a(22) =1036072a(23) =1340352a(24) =1715434a(25) =2173874a(26) =2729822a(27) =3399151a(28) =4199591a(29) =5150868