Number of permutations of [n] avoiding {1423, 1234, 3412}.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =21a(5) =74a(6) =248a(7) =780a(8) =2309a(9) =6483a(10) =17407a(11) =45028a(12) =112921a(13) =275964a(14) =660030a(15) =1550320a(16) =3586449a(17) =8190493a(18) =18500893a(19) =41399992a(20) =91896773a(21) =202564062a(22) =443789172a(23) =967093220a(24) =2097536909a(25) =4530328551a(26) =9748157339a(27) =20905142940a(28) =44695397953a(29) =95295673696