Number of permutations of length n which avoid the patterns 1234, 2431, 4213.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =70a(5) =192a(6) =441a(7) =929a(8) =1870a(9) =3670a(10) =7097a(11) =13600a(12) =25907a(13) =49142a(14) =92911a(15) =175190a(16) =329563a(17) =618681a(18) =1159262a(19) =2168484a(20) =4050003a(21) =7553315a(22) =14068790a(23) =26173531a(24) =48640712a(25) =90304947a(26) =167508064a(27) =310461529a(28) =574989748a(29) =1064197426