Number of length n permutations avoiding (123,{1},{}) and (231,{},{2}).

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =9a(5) =22a(6) =57a(7) =155a(8) =440a(9) =1299a(10) =3977a(11) =12596a(12) =41181a(13) =138711a(14) =480548a(15) =1709714a(16) =6238685a(17) =23319998a(18) =89199763a(19) =348799322a(20) =1393087403a(21) =5678298218a(22) =23603135064a(23) =99984420371a(24) =431347901729