Number of permutations of length n which avoid the patterns 3124, 3421, 4231.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =75a(5) =258a(6) =845a(7) =2649a(8) =8019a(9) =23630a(10) =68216a(11) =193861a(12) =544312a(13) =1514024a(14) =4180488a(15) =11476203a(16) =31358553a(17) =85367436a(18) =231691655a(19) =627259131a(20) =1694678721a(21) =4570645292a(22) =12309288446a(23) =33108960151a(24) =88958761210a(25) =238792953938