I have an Algebra and Cryptography (major) exam coming up this week...?

but the majority of it is going to be number theory and proving etc.....e.g. Let p1, p2, ... pn be distinct primes (where 1, 2 and n are subscript). Show thatp1p2 (where 1 and 2 are subscript) ... pn +1 (where n is subscript)is not divisible by any of the pi's (where i is subscript).Deduce that there are infinately many primes.Has anyone got any suggestions on how I study for exam coming up? Because all proofs for number theory are quite different... and I can't learn every single proof!!! Are there any set patterns that I use for all proofs? Any suggestions would be great!!Thanks