jmc

We can tell that the three-digit number will be 111 times some number $x$ (resulting in 111, 222,...999), so the prime factors of the three-digit number will contain the prime factors of 111, which has prime factorization $3\cdot 37$. The sum of those two prime factors is 40, which means that $x$ is $47-40=7$. So, our answer is $111\cdot 7=\boxed{777}$.