# Another squares problem

How many pairs of distinct positive integers $a, b: (b > a)$ exist such that $(a^2 + 1)(b^2 + 1)$ is a square?
How many pairs of distinct positive integers $a, b: (b > a)$ exist such that $(a^2 + 1)(b^2 + 1)$ is a square?
start with this identity: $(a^2+1)(b^2+1)=(ab \pm 1)^2+(a \mp b)^2.$ (Wink)