project_euler_3.fs

let isPrime (n: int) =
    let max = sqrt (float32 n) |> int 
    let rec check m =
        if m > max then true
        elif n % m = 0 then false        
        else check (m+1)
    check 2
    
let n = 600851475143L //

Seq.init (sqrt (float32 n) |> int) (fun i -> i + 2)
|> Seq.filter (fun x -> n % int64 x = 0L)
|> Seq.filter isPrime
|> Seq.last
|> printfn "%A"