Number of permutations of length n which avoid the patterns 2341, 3421, 4123.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =73a(5) =241a(6) =766a(7) =2399a(8) =7514a(9) =23648a(10) =74706a(11) =236352a(12) =747770a(13) =2364773a(14) =7475960a(15) =23631523a(16) =74699975a(17) =236139689a(18) =746503680a(19) =2359936092a(20) =7460507061a(21) =23584937695a(22) =74558966315a(23) =235702724400a(24) =745125438325