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