Number of permutations with exactly 1 valley which avoid the pattern 1324.

Terms

a(0) =0a(1) =0a(2) =2a(3) =15a(4) =75a(5) =313a(6) =1179a(7) =4161a(8) =14051a(9) =45993a(10) =147195a(11) =463345a(12) =1440723a(13) =4438905a(14) =13582955a(15) =41350977a(16) =125404611a(17) =379228489a(18) =1144370139a(19) =3447856017a(20) =10375942835a(21) =31198607385a(22) =93749962827a(23) =281584384225a(24) =845476670115