**A Mersenne prime is a prime number of the form $2^n−1$. Produce a list
of those n, which are at most 1,000, for which $2^n − 1$ is prime**

I am able to find the list of prime numbers:

```
Select[Table[m = 2^n - 1, {n, Range[1000]}], PrimeQ]

{3, 7, 31, 127, 8191, 131071, 524287, 2147483647...etc.

```

How can I make a list of their corresponding "*n*" values?