Number of permutations of [1..n] which avoid 4231 and 42513.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =23a(5) =102a(6) =495a(7) =2549a(8) =13682a(9) =75714a(10) =428882a(11) =2474573a(12) =14492346a(13) =85926361a(14) =514763279a(15) =3111119358a(16) =18946375767a(17) =116147683902a(18) =716179441293