Function f:{1,2,3,4,5}→{1,2,3,4,5} is said to be nasty if there do not exist distinct a,b∈{1,2,3,4,5} satisfying f(a)=b and f(b)=a. How many nasty functions are there?

Function f:{1,2,3,4,5}→{1,2,3,4,5} is said to be nasty if there do n

1.	Function f:{1,2,3,4,5}→{1,2,3,4,5} is said to be nasty if there do not exist distinct a,b∈{1,2,3,4,5} satisfying f(a)=b and f(b)=a. How many nasty functions are there?
Answer» Function $f : {1, 2, 3, 4, 5} \to {1, 2, 3, 4, 5}$ is said to be nasty if there do not exist distinct $a, b \in {1, 2, 3, 4, 5}$ satisfying $f (a) = b$ and $f (b) = a .$ How many nasty functions are there?