Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, up, up, up.
A177564
Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, up, up, up.
Terms
- a(0) =1a(1) =1a(2) =6a(3) =90a(4) =2520a(5) =112681a(6) =7368841a(7) =663399996a(8) =78683697960
External references
- oeis: A177564