Number of permutations of [n] avoiding {1324, 1342, 3421}.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =21a(5) =75a(6) =259a(7) =853a(8) =2684a(9) =8120a(10) =23782a(11) =67845a(12) =189493a(13) =520359a(14) =1409742a(15) =3778514a(16) =10042552a(17) =26517095a(18) =69668495a(19) =182357337a(20) =476027280a(21) =1240285036a(22) =3227591882a(23) =8393207561a(24) =21819385961a(25) =56722065995a(26) =147485931154a(27) =383621798278a(28) =998279190044