Number of permutations of length n which avoid the patterns 1234, 1342, 2431.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =74a(5) =248a(6) =787a(7) =2389a(8) =7013a(9) =20079a(10) =56417a(11) =156250a(12) =427914a(13) =1161571a(14) =3130892a(15) =8391305a(16) =22387648a(17) =59509600a(18) =157714833a(19) =416978205a(20) =1100298811a(21) =2898861767a(22) =7627745311a(23) =20050436226a(24) =52661977424a(25) =138224905323