Number of permutations of length n which avoid the patterns 1234, 2431, 3241.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =73a(5) =231a(6) =650a(7) =1668a(8) =3987a(9) =9030a(10) =19628a(11) =41333a(12) =84915a(13) =171087a(14) =339408a(15) =665004a(16) =1289881a(17) =2481422a(18) =4741442a(19) =9009137a(20) =17038193a(21) =32096591a(22) =60263770a(23) =112832696a(24) =210754191a(25) =392853778a(26) =731013500a(27) =1358206773a(28) =2520242339