## Hints
For this exercise the following F# feature comes in handy:
- [Sequences](https://docs.microsoft.com/en-us/dotnet/articles/fsharp/language-reference/sequences) are evaluated lazily. They allows you to work with an infinite sequence of values.

Note: to help speedup calculation, you should not check numbers which you know beforehand will never be prime. For more information, see the [Sieve of Eratosthenes](https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes).