Number of permutations of length n which avoid the patterns 4312 and 2143.

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =22a(5) =86a(6) =337a(7) =1295a(8) =4854a(9) =17760a(10) =63594a(11) =223488a(12) =772841a(13) =2635733a(14) =8882042a(15) =29622114a(16) =97901974a(17) =321016826a(18) =1045294921a(19) =3382803539a(20) =10887874254a(21) =34873641228a(22) =111215129370a(23) =353295398148