A333082 Number of permutations sigma of [n] such that all values sigma(k)/k for 1 <= k <= n are pairwise distinct.

1, 1, 1, 5, 13, 79, 345, 2785, 19595, 171141, 1555181, 18998391, 184988197, 2675065491, 35582840563, 490186693669

Offset: 0

Author

Seiichi Manyama, Mar 07 2020

Keywords

• nonn
• more

Links

• Wikipedia, Permutation

Crossrefs

Cf. A333083.

Programs

Mathematica

Table[ Count[ Length[ Union[ #/ Range[n]]] & /@ Permutations[ Range@n], n], {n, 0, 9}] (* Giovanni Resta, Mar 09 2020 *)

Ruby

def A(n)
  (1..n).to_a.permutation.select{|i| (1..n).map{|j| i[j - 1] / j.to_r}.uniq.size == n}.size
end
def A333082(n)
  (0..n).map{|i| A(i)}
end
p A333082(9)

Extensions

a(13)-a(15) from Giovanni Resta, Mar 09 2020