MATH: A nice problem that I found

By Bruno;

As you all know, my favorite subject is number theory, and one thing that always fascinates me is that there are a lot of problems that seem difficult, but actually you just need the right idea. As I don't want to waste a lot of your time talking about me, I'll quickly introduce you the problem the title alludes:

Interesting! It is sensible to think that if we find infinitely many example, we are done with this problem, isn't it? If you're not so keen on math, this idea may sound a little absurd. But trust me, it is not!

Solution:

I said that it wouldn't be absurd, didn't I? But I guess it will be everything for today. See you next week!