Number of permutations of [n] avoiding {1423, 2341, 3124}.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =21a(5) =73a(6) =243a(7) =785a(8) =2511a(9) =8073a(10) =26312a(11) =87257a(12) =294603a(13) =1011602a(14) =3526519a(15) =12456315a(16) =44495535a(17) =160468964a(18) =583421709a(19) =2135814678a(20) =7865015071a(21) =29109558620a(22) =108213772256a(23) =403835324635