Nth Prime Problem complete

exercism/fsharp/nth-prime/NthPrime.fs

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+module NthPrime
+
+let isPrime n = 
+    let stop = int(sqrt(float(n)))
+    seq { 2..stop }
+    |> Seq.exists (fun x -> n % x = 0)
+    |> not
+
+let oddNumbers = Seq.initInfinite (fun i -> i + 2)
+
+let oddPrimes = Seq.filter isPrime oddNumbers
+
+let safeNthPrime n = if n = 1 then 2 else Seq.last (Seq.take n oddPrimes)
+
+let prime nth : int option = if nth = 0 then None else Some(safeNthPrime nth)

exercism/fsharp/nth-prime/NthPrime.fsproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netcoreapp3.0</TargetFramework>
+
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="NthPrime.fs" />
+    <Compile Include="NthPrimeTests.fs" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.6.1" />
+    <PackageReference Include="xunit" Version="2.4.1" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.2" />
+    <PackageReference Include="FsUnit.xUnit" Version="3.9.0" />
+  </ItemGroup>
+
+</Project>

exercism/fsharp/nth-prime/NthPrimeTests.fs

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+// This file was auto-generated based on version 2.1.0 of the canonical data.
+
+module NthPrimeTests
+
+open FsUnit.Xunit
+open Xunit
+
+open NthPrime
+
+[<Fact>]
+let ``First prime`` () =
+    prime 1 |> should equal (Some 2)
+
+[<Fact>]
+let ``Second prime`` () =
+    prime 2 |> should equal (Some 3)
+
+[<Fact>]
+let ``Sixth prime`` () =
+    prime 6 |> should equal (Some 13)
+
+[<Fact>]
+let ``Big prime`` () =
+    prime 10001 |> should equal (Some 104743)
+
+[<Fact>]
+let ``There is no zeroth prime`` () =
+    prime 0 |> should equal None
+

exercism/fsharp/nth-prime/README.md

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+# 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](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).
+
+## 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](https://github.com/fsprojects/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](http://exercism.io/languages/fsharp/resources).
+
+## Source
+
+A variation on Problem 7 at Project Euler [http://projecteuler.net/problem=7](http://projecteuler.net/problem=7)
+