Hi everbody! Well, I've been trying to understand the solution for this problem for a while, but I think I need a little help.

Solutions (all SWERC 2012): http://users.dsic.upv.es/swerc_12/ProblemSet2012/SWERC-2012-solution-outlines.pdf

Yes, it has a pdf with the solution explained. The thing is that there is a mistake (or I can not understand what they mean). They talk about a function SOD(x), which is Sum Of Divisors of x. But the SOD of 12, for example, clearly isn't 3, as they say in the pdf.

I hope someone can give me a hand with it, and if you have some extra topics I can read about, that might help me with this problem, would be great as well!

Thanks in advance.