Prime number

Question

138,215,030 is a product of 3 prime numbers. Which ones?

How am I supposed to calculate this?

Answer 1

    If you think of those prime factorization trees, your number is 13821503 * 10 or 13821503 * 5 * 2. Two out of the 3 of these are prime, so if your question is correct in stating that it can be factored into 3 primes, 13821503 must be the third prime.