Contrapositive and Contradiction · Hard problem

If $n^2$ is not divisible by $4$, then $n$ is odd

If $n^2$ is not divisible by $8$, then $n$ is odd

If $n$ is not divisible by $4$, then $n^2$ is not divisible by $4$

If $n^2$ is divisible by $4$, then $n$ is divisible by $4$