Number of permutations of [n] avoiding {1324, 2341, 3421}.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =21a(5) =73a(6) =238a(7) =726a(8) =2101a(9) =5857a(10) =15926a(11) =42626a(12) =112997a(13) =297861a(14) =782666a(15) =2052958a(16) =5379953a(17) =14091781a(18) =36901646a(19) =96621062a(20) =252971401a(21) =662305301a(22) =1733959342a(23) =4539590666a(24) =11884834161a(25) =31114937393a(26) =81460008218a(27) =213265122686a(28) =558335401141