fsharp-learning/exercism/fsharp/nth-prime

Nth Prime

Given a number n, determine what the nth prime is.

By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6th prime is 13.

If your language provides methods in the standard library to deal with prime numbers, pretend they don’t exist and implement them yourself.

Hints

For this exercise the following F# feature comes in handy:

• 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.

Running the tests

To run the tests, run the command dotnet test from within the exercise directory.

Autoformatting the code

F# source code can be formatted with the Fantomas tool.

After installing it with dotnet tool restore, run dotnet fantomas . to format code within the current directory.

Further information

For more detailed information about the F# track, including how to get help if you’re having trouble, please visit the exercism.io F# language page.

Source

A variation on Problem 7 at Project Euler http://projecteuler.net/problem=7