Number of permutations of length n which avoid the patterns 1234, 2413, 3241.

Terms

a(0) =1a(1) =2a(2) =6a(3) =21a(4) =72a(5) =230a(6) =689a(7) =1970a(8) =5460a(9) =14833a(10) =39790a(11) =105890a(12) =280367a(13) =739878a(14) =1948186a(15) =5121973a(16) =13451620a(17) =35299782a(18) =92580429a(19) =242705586a(20) =636062896a(21) =1666534337a(22) =4365640346a(23) =11434584546a(24) =29946505947a(25) =78421715110a(26) =205352199014