Number of permutations of length n which avoid the patterns 2341, 3214, 4123.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =70a(5) =212a(6) =611a(7) =1712a(8) =4712a(9) =12815a(10) =34576a(11) =92764a(12) =247819a(13) =659840a(14) =1752170a(15) =4642567a(16) =12278546a(17) =32424408a(18) =85514335a(19) =225286086a(20) =592967054a(21) =1559508979a(22) =4098803122a(23) =10766657412a(24) =28268032251a(25) =74187679124a(26) =194632590500