project euler problem 152

Writing 1/2 as a sum of inverse squares

I checked my old code, it looks like OK. I used some sort of brute force method(but I tried my best to minimize the number of candidates, try to group the candidates, and consider large ones first). It only takes 1 second to get the answer. But after I changed the number limit from 80 to 100, I can not get the answer in 80 seconds! So it definitely needs to be optimized.

I am still working on it ... 

The best solution is on page 2 in the discussion thread.