並列化した素数計算プログラム

ParallelPrimeNumber.cs

Console.Write("求めたい値を入力 >");
string target_str = Console.ReadLine();
long target = long.Parse(target_str);

System.Diagnostics.Stopwatch sw = new System.Diagnostics.Stopwatch();
bool flg = false;
sw.Start();
Parallel.For(2, 8202464, (i, loopstate) => {
    if(target % i == 0)
    {
        flg = true;
        loopstate.Break();
    }
});
sw.Stop();
if (flg)
{
    Console.WriteLine(target + "は素数ではない");
    Console.WriteLine("処理時間" + sw.ElapsedMilliseconds + "ms");
}
else
{
    Console.WriteLine(target + "は素数");
    Console.WriteLine("処理時間" + sw.ElapsedMilliseconds + "ms");
}