Kenneth Rosen Edition 7 Exercise 2.3 Question 20 (Page No. 153)

Question

Give an example of a function from $N$ to $N$ that is

1. one-to-one but not onto.
2. onto but not one-to-one.
3. both onto and one-to-one (but different from the identity function).
4. neither one-to-one nor onto.