Number of permutations of length n which avoid the patterns 2143, 2431, 3124.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =73a(5) =244a(6) =794a(7) =2553a(8) =8179a(9) =26192a(10) =83906a(11) =268883a(12) =861815a(13) =2762484a(14) =8855204a(15) =28385839a(16) =90992639a(17) =291683062a(18) =935010104a(19) =2997239539a(20) =9607859097a(21) =30798658994a(22) =98727239296a(23) =316477019741