Number of permutations of length n which avoid the patterns 1324, 2431, 4123.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =72a(5) =229a(6) =686a(7) =1972a(8) =5514a(9) =15131a(10) =40986a(11) =110013a(12) =293376a(13) =778678a(14) =2059646a(15) =5434009a(16) =14309508a(17) =37628165a(18) =98841306a(19) =259426800a(20) =680498610a(21) =1784183887a(22) =4676276006a(23) =12253079101a(24) =32099813532a(25) =84080037314a(26) =220207603686