Number of permutations of length n which avoid the patterns 1234, 2431, 4132.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =71a(5) =209a(6) =545a(7) =1348a(8) =3270a(9) =7908a(10) =19201a(11) =46918a(12) =115407a(13) =285642a(14) =711031a(15) =1779289a(16) =4474537a(17) =11304830a(18) =28685778a(19) =73083753a(20) =186888321a(21) =479511547a(22) =1234006566a(23) =3184091383a(24) =8234890726a(25) =21340207949a(26) =55396690600a(27) =144013075958