Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, down, up, down.
A177561
Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, down, up, down.
Terms
- a(0) =1a(1) =6a(2) =74a(3) =1730a(4) =62340a(5) =3258982a(6) =232475188a(7) =21711360018
External references
- oeis: A177561