Since they mention prime numbers, the fun thing about number theory and prime numbers is thanks to factorisation, prime numbers kind of made up ever other numbers. Since we know there are infinite number of prime number, thanks to Euclid, we have this series of numbers that basically construct every other number. If you ponder it a little, it's kind of amazing. As the number of numbers increase, the gap between prime also increases as the primes start to fill up more gaps between one prime to the next. You would think there is a limit to prime, as one would imagine at some point, there are so many primes that they cover the entire number line, preventing those numbers from being factorised, but apparent there isn't.