Let be a prime and a positive integer, .

So you see that the only prime such that is .

Let be an integer such that , and its unique decomposition in a product of primes, with and . Then, for all has to divide , and a consequence is .

so , and since is odd, that means .

If , that's ok; if , and can't divide and

As you may see, .

Furthermore, .

Conclusion: the integers such that are the elements of