ParallelTest C#

ParallelTest

using System;
using System.Linq;
using System.Diagnostics;

namespace ParallelTest
{
    public class Program
    {
        public static void Main()
        {
            const int max = 10000000;


            var startTime = Stopwatch.StartNew();

            var pt = new Program();
            int primes = pt.countPrimes(max);
            Console.WriteLine(primes);

            startTime.Stop();
            
            Console.WriteLine(startTime.Elapsed.TotalMilliseconds.ToString());

        }

        private int countPrimes(int max)
        {

            return Enumerable
                    .Range(1, max)
                    .AsParallel()
                    .Where(x => isPrime(x))
                    .Count();

        }

        private bool isPrime(long n)
        {
            if (n < 2) return false;
            if (n == 2 || n == 3) return true;
            if (n % 2 == 0 || n % 3 == 0) return false;
            long sqrtN = (long)Math.Sqrt(n) + 1;
            for (long i = 6L; i <= sqrtN; i += 6)
            {
                if (n % (i - 1) == 0 || n % (i + 1) == 0) return false;
            }
            return true;
        }

    }

}