Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, down, up.

A177557

Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, down, up.

Terms

    a(0) =1a(1) =5a(2) =55a(3) =1062a(4) =31147a(5) =1313796a(6) =75373533a(7) =5661748406a(8) =539467979009

External references