# Project Euler – Problem 10 Solution

Yan Cui

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#### Problem

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

Find the sum of all the primes below two million.

#### Solution

```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#.