Number of permutations p of [2n] having at least one index i with |p(i)-i| = n.
A306675
Number of permutations p of [2n] having at least one index i with |p(i)-i| = n.
Terms
- a(0) =0a(1) =1a(2) =15a(3) =455a(4) =25487a(5) =2293839a(6) =302786759a(7) =55107190151
External references
- oeis: A306675