Number of permutations of length n which avoid the patterns 2413, 3421, 4123.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =73a(5) =245a(6) =804a(7) =2617a(8) =8511a(9) =27709a(10) =90283a(11) =294231a(12) =958826a(13) =3124175a(14) =10178664a(15) =33160777a(16) =108030912a(17) =351937426a(18) =1146512182a(19) =3734982701a(20) =12167348792a(21) =39637060036a(22) =129123584284a(23) =420638265356