Number of permutations of length n which avoid the patterns 2341, 4213.

Terms

a(0) =1a(1) =2a(2) =6a(3) =22a(4) =86a(5) =336a(6) =1290a(7) =4870a(8) =18164a(9) =67234a(10) =247786a(11) =911120a(12) =3346618a(13) =12286942a(14) =45104548a(15) =165573482a(16) =607817410a(17) =2231360192a(18) =8191763970a(19) =30074097062a(20) =110410946820a(21) =405353571346