We will find out if (a,b,613) is a Pythagorean triple.
If so then (a,b,613) = (m²-n²,2mn,m²+n²)
b+613 = 2mn+m²+n²
b+613 = m²+2mn+n²
b+613 = (m+n)²
We find the next perfect square greater than 613,
and see if that works. √613 = 24.7588...
So the next perfect square is 25² = 625
If b+613 = 625
b = 612
Then
So it works, and a+b = 35+612 = 647
Edwin