Number of permutations of length n which avoid the patterns 1324, 3421, 4123.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =70a(5) =203a(6) =517a(7) =1187a(8) =2504a(9) =4921a(10) =9107a(11) =16009a(12) =26922a(13) =43567a(14) =68177a(15) =103591a(16) =153356a(17) =221837a(18) =314335a(19) =437213a(20) =598030a(21) =805683a(22) =1070557a(23) =1404683a(24) =1821904a(25) =2338049a(26) =2971115a(27) =3741457a(28) =4671986a(29) =5788375