Number of permutations of length n which avoid the patterns 1423, 3124, 3421.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =71a(5) =219a(6) =626a(7) =1698a(8) =4452a(9) =11428a(10) =28966a(11) =72907a(12) =182915a(13) =458590a(14) =1150877a(15) =2894324a(16) =7299391a(17) =18468191a(18) =46885660a(19) =119437550a(20) =305268086a(21) =782671392a(22) =2012470416a(23) =5188157511a(24) =13406252581a(25) =34712884554a(26) =90042441271a(27) =233921270608