Challenge34: Calculate Euler's totient function phi(m).
Challenge35: Determine the prime factors of a given positive integer.
Challenge36: Determine the prime factors of a given positive integer (2).
Challenge37: Calculate Euler's totient function phi(m) (improved).
Challenge38: Compare the two methods of calculating Euler's totient function.
Removing unnecessary type
Challenge39: A list of prime numbers.
Challenge40: Goldbach's conjecture.