## Squarefree Numbers

### Problem 193

A positive integer `n` is called squarefree, if no square of a prime divides `n`, thus 1, 2, 3, 5, 6, 7, 10, 11 are squarefree, but not 4, 8, 9, 12.

How many squarefree numbers are there below 2^{50}?

A positive integer `n` is called squarefree, if no square of a prime divides `n`, thus 1, 2, 3, 5, 6, 7, 10, 11 are squarefree, but not 4, 8, 9, 12.

How many squarefree numbers are there below 2^{50}?