Difference of squares problem done

exercism/fsharp/difference-of-squares/DifferenceOfSquares.fs

+module DifferenceOfSquares
+
+let square n = pown n 2
+
+let squareOfSum (number: int): int = square ([1..number] |> List.sum)
+
+let sumOfSquares (number: int): int = [1..number] |> List.sumBy square
+
+let differenceOfSquares (number: int): int = abs ((sumOfSquares number) - (squareOfSum number))

exercism/fsharp/difference-of-squares/DifferenceOfSquares.fsproj

+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>netcoreapp3.0</TargetFramework>
+
+    <IsPackable>false</IsPackable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="DifferenceOfSquares.fs" />
+    <Compile Include="DifferenceOfSquaresTests.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="3.8.1" />
+  </ItemGroup>
+
+</Project>

exercism/fsharp/difference-of-squares/DifferenceOfSquaresTests.fs

+// This file was auto-generated based on version 1.2.0 of the canonical data.
+
+module DifferenceOfSquaresTests
+
+open FsUnit.Xunit
+open Xunit
+
+open DifferenceOfSquares
+
+[<Fact>]
+let ``Square of sum 1`` () =
+    squareOfSum 1 |> should equal 1
+
+[<Fact>]
+let ``Square of sum 5`` () =
+    squareOfSum 5 |> should equal 225
+
+[<Fact>]
+let ``Square of sum 100`` () =
+    squareOfSum 100 |> should equal 25502500
+
+[<Fact>]
+let ``Sum of squares 1`` () =
+    sumOfSquares 1 |> should equal 1
+
+[<Fact>]
+let ``Sum of squares 5`` () =
+    sumOfSquares 5 |> should equal 55
+
+[<Fact>]
+let ``Sum of squares 100`` () =
+    sumOfSquares 100 |> should equal 338350
+
+[<Fact>]
+let ``Difference of squares 1`` () =
+    differenceOfSquares 1 |> should equal 0
+
+[<Fact>]
+let ``Difference of squares 5`` () =
+    differenceOfSquares 5 |> should equal 170
+
+[<Fact>]
+let ``Difference of squares 100`` () =
+    differenceOfSquares 100 |> should equal 25164150
+

exercism/fsharp/difference-of-squares/README.md

+# Difference Of Squares
+
+Find the difference between the square of the sum and the sum of the squares of the first N natural numbers.
+
+The square of the sum of the first ten natural numbers is
+(1 + 2 + ... + 10)² = 55² = 3025.
+
+The sum of the squares of the first ten natural numbers is
+1² + 2² + ... + 10² = 385.
+
+Hence the difference between the square of the sum of the first
+ten natural numbers and the sum of the squares of the first ten
+natural numbers is 3025 - 385 = 2640.
+
+You are not expected to discover an efficient solution to this yourself from
+first principles; research is allowed, indeed, encouraged. Finding the best
+algorithm for the problem is a key skill in software engineering.
+
+## Hints
+For this exercise the following F# features come in handy:
+- The [range operator](https://msdn.microsoft.com/en-us/visualfsharpdocs/conceptual/operators.%5B-..-%5D%5B%5Et%5D-function-%5Bfsharp%5D) allows you to succinctly create a range of values.
+- [List.sumBy](https://msdn.microsoft.com/en-us/visualfsharpdocs/conceptual/list.sumby%5B't,%5Eu%5D-function-%5Bfsharp%5D) is a condensed format to apply a function to a list and then sum the results.
+
+
+## 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
+
+Problem 6 at Project Euler [http://projecteuler.net/problem=6](http://projecteuler.net/problem=6)
+