1. The problem statement, all variables and given/known data The problem (and its solution) are attached in TheProblemAndSolution.jpg. Specifically, I am referring to problem (c). 2. Relevant equations Set theory. Union. Integers. Prime numbers. 3. The attempt at a solution I see how we have all multiples of all prime numbers in the union of the sets, but I can't see how “every positive integer except 1 is a multiple of at least one prime number”. If I could intuitively grasp the sentence I just quoted, then I can see how to get to the final result. Any help in getting me to intuitively understand the part I quoted would be greatly appreciated!