Number of permutations of length n which avoid the patterns 1234, 2431, 4231.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =73a(5) =232a(6) =654a(7) =1639a(8) =3705a(9) =7678a(10) =14798a(11) =26841a(12) =46257a(13) =76324a(14) =121318a(15) =186699a(16) =279313a(17) =407610a(18) =581878a(19) =814493a(20) =1120185a(21) =1516320a(22) =2023198a(23) =2664367a(24) =3466953a(25) =4462006a(26) =5684862a(27) =7175521a(28) =8979041a(29) =11145948