Number of permutations of [n] avoiding {1324, 2413, 3421}.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =21a(5) =73a(6) =241a(7) =754a(8) =2252a(9) =6471a(10) =18003a(11) =48736a(12) =128878a(13) =333949a(14) =850061a(15) =2130078a(16) =5263536a(17) =12845251a(18) =30998743a(19) =74055916a(20) =175309058a(21) =411566361a(22) =958923057a(23) =2218787146a(24) =5101322596a(25) =11660165503a(26) =26508001691a(27) =59961770424a(28) =135006257622a(29) =302660977141