Number of permutations of length n which avoid the patterns 4123 and 2341.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =22a(5) =87a(6) =348a(7) =1374a(8) =5335a(9) =20462a(10) =77988a(11) =296787a(12) =1130969a(13) =4321239a(14) =16559467a(15) =63633036a(16) =245113705a(17) =946140207a(18) =3658715938a(19) =14170931497a(20) =54966429252a(21) =213487762758a(22) =830195102515