常用演算法(C#): 判斷素數的演算法

using System;
using System.Collections.Generic;
using System.Text;

namespace ExPrimeNumber
{
    class PrimeNumber
    {
        public bool primeNumber(int n)
        {
            bool b = true;
            if (n == 1 || n == 2)
                b = true;
            else
            {
                int sqr = Convert.ToInt32(Math.Sqrt(n));
                for (int i = sqr; i > 2; i--)
                {
                    if (n % i == 0)
                    {
                        b = false;
                    }
                }
            }
            return b;
        }
        static void Main(string[] args)
        {
            Console.Write("請輸入一個數：");
            int n = Convert.ToInt32(Console.ReadLine ());
            PrimeNumber p=new PrimeNumber ();
            bool b=p.primeNumber(n);
            if (b)
                Console.WriteLine("{0}是素數",n);
            else
                Console.WriteLine("{0}不是素數",n);

        }
    }
}