1. The problem statement, all variables and given/known data Find x such that phi(x) = 5,000,000, where phi(x) is Euler's function. 2. Relevant equations I know that if x is prime, then phi(x) = x-1. Also, phi(pk) = pk - pk-1 = pk * (1 - 1/p). 3. The attempt at a solution Since 5,000,001 is not a prime number (divisible by 3), I know that x is not a prime number, and so x must be composite. Past this, I'm not really sure how to begin. The book that I'm using (Elementary Number Theory by Burton) includes lots of example for finding phi(whatever), but none for how to solve phi(x) = whatever. A nudge in the right direction would be helpful!