P37

P37 - calculate Euler's totient function phi(m) (improved).

Euler's so-called totient function phi(m) is defined as the number of positive integers r (1 <= r < m) that are coprime to m. We let phi(1) = 1.

From the definition of P34, we can see that phi(m) is equal to m * (1 - 1/p1) * (1 - 1/p2) * (1 - 1/p3) * ... where p1, p2, p3, ... are the prime factors of m.

Note that we need to use the primeFactors function from P36.