Number of permutations of length n which avoid the patterns 1243, 4132, 4321.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =74a(5) =237a(6) =668a(7) =1667a(8) =3750a(9) =7743a(10) =14898a(11) =27033a(12) =46698a(13) =77369a(14) =123672a(15) =191639a(16) =288998a(17) =425499a(18) =613278a(19) =867261a(20) =1205610a(21) =1650213a(22) =2227220a(23) =2967627a(24) =3907910a(25) =5090711a(26) =6565578a(27) =8389761a(28) =10629066a(29) =13358769