How to search for maths?

I know that numbers of the form b^n+1 are divisible (with certain constraints) only by factors == 1 (mod n), and wanted to find a proof of that, and a characterization of the constraints.

I remembered that the Cunningham project searched for factors of such numbers, so I headed there to search for suitable terminology to search on, but couldn't find any (though I did find the notation b^n as opposed to, say, x^y).

Wikipedia's article on Fermat numbers mentions the property for that case, and that the property was proven by Euler, but provides no further detail. I couldn't find the property mentioned at all in the PlanetMath pages on Fermat numbers.

And every search engine I know to try ignores or strips out operators such as ^ and +. Even if they didn't, there is no guarantee that the pages I'm looking for use "b" and "n" for the variables.

So, how do you search for something like this?

I had a similar question the other day, relating to solutions of p^4+1=2q^2, and ended up asking on mathoverflow. I got a solution there, but no help on the "how to search" side-question.

Hugo