Möbius function and intervals
Problem 464Published on Sunday, 23rd March 2014, 01:00 am; Solved by 167; Difficulty rating: 60%
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).