Number of permutations of length n which avoid the patterns 2143, 2341, 4213.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =71a(5) =222a(6) =652a(7) =1838a(8) =5053a(9) =13682a(10) =36697a(11) =97814a(12) =259585a(13) =686709a(14) =1812257a(15) =4773804a(16) =12557136a(17) =32994311a(18) =86620279a(19) =227256969a(20) =595933506a(21) =1562111927a(22) =4093542416a(23) =10724799901a(24) =28093431826a(25) =73580651302a(26) =192698841652