/// <summary>

    /// 素数帮忙类

    /// 本类是从.net源码 类 internal static class HashHelpers 类里抽取相应的代码

    /// https://referencesource.microsoft.com/#mscorlib/system/collections/hashtable.cs,e8668bf19da49963

    /// Hashtable.cs里

    /// </summary>

    public class PrimeHelper

    {

        /// <summary>

        /// 给定一些素数(除了2)

        /// </summary>

        public static readonly int[] Primes = {

            , , , , , , , , , , , , , , , , , , , , , , ,

            , , , , , , , , , , , , , , ,

            , , , , , , , , , , , , ,

            , , , , , , , , , , , ,

            , , , , , , , , };

        /// <summary>

        /// 判断是否是素数

        /// </summary>

        /// <param name="candidate"></param>

        /// <returns></returns>

        public static bool IsPrime(int candidate)

        {

            //偶数当然不是素数

            if ((candidate & ) != )

            {

                int limit = (int)Math.Sqrt(candidate);

                for (int divisor = ; divisor <= limit; divisor += )

                {

                    if ((candidate % divisor) == )

                        return false;

                }

                return true;

            }

            //2是素数

            return (candidate == );

        }

        /// <summary>

        /// 大于给定数的最小素数

        /// </summary>

        /// <param name="min"></param>

        /// <returns></returns>

        public static int GetPrime(int min)

        {

            if (min < )

            {

                throw new ArgumentException("给定数必须是自然数");

            }

            //先从给定数组里找

            foreach (int prime in Primes)

            {

                if (prime >= min)

                {

                    return prime;

                }

            }

            //给定数组里没有相应的素数,则循环找

            //如果min是偶数,则起始值为加1,否则起始值为本身

            for (int i = (min | ); i < Int32.MaxValue; i += )

            {

                if (IsPrime(i) )

                    return i;

            }

            return min;

        }

        /// <summary>

        /// 获取最小素数(2除外)

        /// </summary>

        /// <returns></returns>

        public static int GetMinPrime()

        {

            return Primes[];

        }

    }