def problem464():
    """


    The Möbius function, denoted μ(n), is defined as:

         • μ(n) = (-1)^ω(n) if n is squarefree (where ω(n) is the number of
           distinct prime factors of n)
         • μ(n) = 0 if n is not squarefree.

       Let P(a,b) be the number of integers n in the interval [a,b] such that
       μ(n) = 1.
       Let N(a,b) be the number of integers n in the interval [a,b] such that
       μ(n) = -1.
       For example, P(2,10) = 2 and N(2,10) = 4.

       Let C(n) be the number of integer pairs (a,b) such that:

         • 1 ≤ a ≤ b ≤ n,
         • 99·N(a,b) ≤ 100·P(a,b), and
         • 99·P(a,b) ≤ 100·N(a,b).

       For example, C(10) = 13, C(500) = 16676 and C(10 000) = 20155319.

       Find C(20 000 000).
    """
    pass
