Square-free integer

A square-free integer is a number which is not divisible by any square numbers other than 1. In other words, each prime number that appears in its prime factorization appears exactly once.
For example, formula_1 is square-free. However, formula_2 is not square-free: it is divisible by formula_3, and the power of formula_4 in the prime factorization is to a power larger than one.