a really difficult math riddle

I don't. I had been looking at:

x, x+1 are relatively prime
y, y+1 are relatively prime
y, y^2+1 are relatively prime
y+1, y^2+1 are relatively prime if y is even - they have 2 as a common factor if y is odd

but didn't get anywhere.

How about posting the answer?

Here's a site with a solution (small font)
http://www.mat.itu.edu.tr/gungor/IMO/www.kalva.demon.co.uk/rsoln/rsoln89.html

come on markr, i am sure you could figure it out by yourself. i was close to give you another hint but since you found out the solution i guess it won't help.

I wouldn't have gotten that.