Proof Writing · Medium problem

$n$ is divisible by $6$ and $n$ is not divisible by $3$.

If $n$ is not divisible by $6$, then $n$ is not divisible by $3$.

If $n$ is not divisible by $3$, then $n$ is not divisible by $6$.

If $n$ is divisible by $3$, then $n$ is divisible by $6$.