Challenge: sum of squares. Let's break 299

[Didier Lachieze]

I have a program that finds the solution for the sequence 1 to 15 in 2 seconds on my Prime, but then it takes 45 seconds for the sequence 1 to 25.
So it needs a significant optimization to reach 299.

Solution for 1 to 25 is:

Code:

spoiler










{2,23,13,12,24,25,11,14,22,3,1,8,17,19,6,10,15,21,4,5,20,16,9,7,18}