# Perfect Squares

Sergei chooses two different natural numbers $$a$$ and $$b$$. He writes four numbers in a notebook: $$a$$, $$a+2$$, $$b$$ and $$b+2$$.

He then writes all six pairwise products of the numbers of notebook on the blackboard.

What is the maximum number of perfect squares on the blackboard?

Assumption: Natural numbers don't include zero.

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