private static void Main(string[] args)
{
const double targetNumber = 600851475143;
var sieveOfEratosthenes = new SieveOfEratosthenes((long) Math.Sqrt(targetNumber));
foreach (long l in sieveOfEratosthenes.Primes().Reverse().Where(l => targetNumber%l == 0))
{
Console.WriteLine(l);
break;
}
Console.ReadLine();
}
static void Main(string[] args)
{
long elementAt = new SieveOfEratosthenes(500000).Primes().ElementAt(10000);
Console.WriteLine(elementAt);
Console.ReadLine();
}