C#生成18位以内的唯一的纯数字

方法：使用13位的当前时间的时间戳，在加上几个随机数

public static string GetTimestamp()
        {
            TimeSpan ts = DateTime.Now.ToUniversalTime() - new DateTime(1970, 1, 1);//ToUniversalTime()转换为标准时区的时间,去掉的话直接就用北京时间
            //随机数
            string strRandomResult = NextRandom(1000, 1).ToString();

            string randonTime=(long)ts.TotalMilliseconds+ strRandomResult;//13位当前时间戳+4位随机数
            return randonTime; 
        }

        public static int NextRandom(int numSeeds, int length)
        {
            // Create a byte array to hold the random value.  
            byte[] randomNumber = new byte[length];
             // Create a new instance of the RNGCryptoServiceProvider.  
             System.Security.Cryptography.RNGCryptoServiceProvider rng = new System.Security.Cryptography.RNGCryptoServiceProvider();
            // Fill the array with a random value.  
            rng.GetBytes(randomNumber);
            // Convert the byte to an uint value to make the modulus operation easier.  
            uint randomResult = 0x0;
             for (int i = 0; i<length; i++)
            {
                 randomResult |= ((uint) randomNumber[i] << ((length - 1 - i) * 8));
             }
             return (int) (randomResult % numSeeds) + 1;
        }

运行结果（最后三位为随机数）：