Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, down, down.
A177556
Number of permutations of 2 copies of 1..n avoiding adjacent step pattern up, down, down.
Terms
- a(0) =1a(1) =6a(2) =78a(3) =1735a(4) =59246a(5) =2885772a(6) =190320239a(7) =16347310234
External references
- oeis: A177556