Prove that there are exists two denumerable sets $A and B$ such that ${ab| a \in A, b \in B}$ is enumerable.

Question

Prove that there are exists two denumerable sets $A$ and $B$: {$a*b| a \in A, b \in B$}

Set is denumerable if we have an algorithm which can output all elements from this set in finite time. Set is enumerable if we can't find this algorythm