Project Euler – Problem 10 Solution


The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17.

Find the sum of all the primes below two million.



open System

let findFactorsOf(n:int64) =
    let upperBound = int64(Math.Sqrt(double(n)))
    [2L..upperBound] |> Seq.filter (fun x -> n % x = 0L)

let isPrime(n:int64) = findFactorsOf(n) |> Seq.length = 0

let primeSequence max = seq { for n in 2L..max do if isPrime(n) then yield n }
let sum = primeSequence 1999999L |> Seq.sum

Yet another prime number related problem, and I’ve borrowed the findFactorsOf and isPrime functions from the problem 3 solution here.

The only interesting bit of code here is the primeSequence function, which generates a sequence of prime numbers equal or greater than 2, up to the specified max using a for … in loop. The for…in loop is basically the same as a foreach (var .. in ..) loop in C#.

Yan Cui

I’m an AWS Serverless Hero and the author of Production-Ready Serverless. I have run production workload at scale in AWS for nearly 10 years and I have been an architect or principal engineer with a variety of industries ranging from banking, e-commerce, sports streaming to mobile gaming. I currently work as an independent consultant focused on AWS and serverless.

You can contact me via Email, Twitter and LinkedIn.

Hire me.