Number of permutations of length n which avoid the patterns 1324 and 4231.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =22a(5) =86a(6) =336a(7) =1282a(8) =4758a(9) =17234a(10) =61242a(11) =214594a(12) =744594a(13) =2566594a(14) =8809442a(15) =30157826a(16) =103082050a(17) =352045314a(18) =1201795970a(19) =4101913602a(20) =13999868162a(21) =47782800386a(22) =163095158274a(23) =556717514754