Find thenumber of all onto functions from the set {1, 2, 3, … , n)to itself.
Ontofunctions from the set {1, 2, 3, … ,n} to itself issimply a permutation on n symbols 1, 2, …, n.
Thus, thetotal number of onto maps from {1, 2, … , n} to itselfis the same as the total number of permutations on n symbols1, 2, …, n, which is n.