半质数

using System;
public class Test
{
    public static int howmany(int x, int y)
    {
        int count = 0;
        for (int i = x; i < y; i++)
        {
            if (isSemiPrimer(i))
            {
                count++;
            }
        }
        return count;
    }
    public static void Main()
    {
        DateTime dateStart = DateTime.Now;
        Console.WriteLine(howmany(1, 2000000));
        TimeSpan span = DateTime.Now - dateStart;
        Console.WriteLine(span.TotalSeconds.ToString());
    }
    public static bool isPrime(int x)
    {
        for (int i = 2; i <= Math.Sqrt((double)x); i++)
        {
            if (x % i == 0)
            {
                return false;
            }
        }
        return true;
    }
    public static bool isSemiPrimer(int x)
    {
        for (int i = 2; i <= Math.Sqrt((double)x); i++)
        {
            if (x % i == 0)
            {
                return isPrime(x / i) && isPrime(i);
            }
        }
        return false;
    }
}

半质数

原文：http://blog.csdn.net/a120705230/article/details/19307247