Number of permutations of [n] avoiding {2143, 3142, 1234}.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =21a(5) =73a(6) =247a(7) =821a(8) =2704a(9) =8868a(10) =29030a(11) =94960a(12) =310531a(13) =1015359a(14) =3319829a(15) =10854379a(16) =35488838a(17) =116031978a(18) =379370276a(19) =1240362982a(20) =4055405209a(21) =13259272613a(22) =43351600979a(23) =141739396705a(24) =463421329340