Number of permutations of length n which avoid the patterns 231, 12534.

Terms

a(0) =1a(1) =2a(2) =5a(3) =14a(4) =41a(5) =121a(6) =355a(7) =1032a(8) =2973a(9) =8496a(10) =24111a(11) =68017a(12) =190885a(13) =533294a(14) =1484021a(15) =4115186a(16) =11375765a(17) =31358377a(18) =86223943a(19) =236540916a(20) =647556621a(21) =1769374932a(22) =4826148315a(23) =13142564449a(24) =35736448201a(25) =97037995226a(26) =263156279525a(27) =712795854422