How many functions f:{1,2,3,4,5}→{1,2,3,4,5}f: \{1, 2, 3, 4, 5\} \to \{1, 2, 3, 4, 5\}f:{1,2,3,4,5}→{1,2,3,4,5} are strictly increasing? (i.e., x<y ⟹ f(x)<f(y)x < y \implies f(x) < f(y)x<y⟹f(x)<f(y))
1
5
10
120