99 problems - python - 34

Calculate Euler's totient function phi(m). 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. Example: m = 10: r = 1,3,7,9; thus phi(m) = 4. Note the special case: phi(1) = 1.

# using coprime defined previously
def totient_phi(m):
    if m == 1:
        return 1
    return len([r for r in range(1,m) if coprime(r,m)])