#### Problem

*The sum of the squares of the first ten natural numbers is,*

*1*^{2} + 2^{2} + … + 10^{2} = 385

*The square of the sum of the first ten natural numbers is,*

*(1 + 2 + … + 10)*^{2} = 55^{2} = 3025

*Hence the difference between the sum of the squares of the first ten natural numbers and the square of the sum is 3025 – 385 = 2640.*

*Find the difference between the sum of the squares of the first one hundred natural numbers and the square of the sum.*

#### Solution

let numbers = [|1..100|]
let sumOfSquares = numbers |> Array.map (fun x -> x * x) |> Array.sum
let sum = numbers |> Array.sum
let squareOfSum = sum * sum
let diff = squareOfSum – sumOfSquares

here’s without defining any functions, but same approach.

(List.sum [1..100] |> (fun x -> x*x)) – (List.map (fun x -> x*x)[1..100] |> List.sum)