Write a program that converts a number to a string, the contents of which depends on the number's prime factors.
- If the number contains 3 as a prime factor, output 'Pling'.
- If the number contains 5 as a prime factor, output 'Plang'.
- If the number contains 7 as a prime factor, output 'Plong'.
- If the number does not contain 3, 5, or 7 as a prime factor, just pass the number's digits straight through.