The difficulty and the required run time vary a lot starting from problem 150 or so. This one seems particularly difficult (it's rated at 85% difficulty, which

The difficulty and the required run time vary a lot starting from problem 150 or so. This one seems particularly difficult (it's rated at 85% difficulty, which is also the highest I've managed to solve). The problem here is that the search space is not 10^10, but higher, since if you iterate over k you don't know which values of m or n need to be tested. For m=1 it's clear that you can just use Pythagorean triples, but for bigger values I don't know if there is a reliable procedure to generate solutions.