[agazso]

I gave a similar solution in the blog comments, but instead of sum of squares I used the product of the numbers. We used to give similar puzzles to candidates on job interviews.

[fizx]

I don't think the product of the numbers solution is linear. Multiplication gets harder as numbers get bigger.

[agazso]

Yeah, you are right. The parent has the right solution, but I already sent my comment to the original post.