a) Give an example of a one-to-one function f:N->N (the function f, from the natural numbers to the natural numbers) that does not map N onto N.

Can I use f(n) = 2n, because that uses all of the n's in N, and each f(n) has only one n going to it, but it doesn't "cover" all of N?

b) Given an example of a function f mapping N onto N that is not a one-to-one function.

I'm drawing a blank here.

c) Give an example of a function f:N->N that is not one-to-one and does not map onto N.

Can I use f(n) = 1? This doesn't cover N, and isn't one-to-one because all the n's go to 1.

Thanks in advance!