"This example uses the simplest possible set of prime number — 1, 3, and 7." 1 is not a prime number. Also, the "simplest" possible set of primes would be 2, 3

"This example uses the simplest possible set of prime number — 1, 3, and 7." 1 is not a prime number. Also, the "simplest" possible set of primes would be 2, 3, and 5.