Project Euler — Problem 6 Solution

Problem

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

12 + 22 + … + 102 = 385

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

(1 + 2 + … + 10)2 = 552 = 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