I've created a (very) simple solution for Project Euler problem 6:Project Euler Problem 6: Sum square differenceThe 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: \$25164150\$To solve this in F# was pretty simple: I simply declared a function square which would multiply an x by itself, then a function which would run through a list of numbers and add the square of the sum of them, and subtract the sum of the squares of each.let square x =    x * xlet calcDiffSquareSumFromSumSquares list =     (list |> List.sum |> square) - (list |> List.sumBy square)printfn Solution to Project Euler 6: %i (calcDiffSquareSumFromSumSquares [ 1 .. 100 ])On this one, I'm particularly curious if there's a functional way to run through the list only once, calculate the total sum, and calculate the squares of sums so that I wouldn't need to use two sum methods.
Project Euler 6: Difference between sum of squares and square of sum
programming challenge;functional programming;f#
Looks good to me.Couple of things to consider though:You could split out two functions, squareOfSum and sumOfSquares. I think that would make it a little easier to read.You could make the functions more general by using Seq.sum/Sum.sumBy instead of List.sum/List.sumBy.While you could use fold, as joranvar mentioned, I think this would make the program much less clear and I would not recommend it (except as an exercise for learning about folds).There is another way to attack the problem, by using the two identities\begin{align}1 + 2 + 3 + \cdots + n &= \frac{n(n + 1)}{2}, \quad \text{and} \\1^2 + 2^2 + 3^2 + \cdots + n^2 &= \frac{n(n+1)(2n+1)}{6}.\end{align}