Number of permutations of length n which avoid the patterns 1243, 4123, 4213.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =75a(5) =262a(6) =890a(7) =2949a(8) =9575a(9) =30590a(10) =96486a(11) =301269a(12) =933171a(13) =2872102a(14) =8794946a(15) =26822901a(16) =81539855a(17) =247232702a(18) =748061070a(19) =2259653349a(20) =6816525435a(21) =20540701510a(22) =61842968906a(23) =186063857829a(24) =559486534391