我想要一个永远唯一的数字，我想出了下面的代码，它生成一个数字，并添加一个校验位到它的结尾，我想知道这个代码有多可靠？

public void GenerateUniqueNumber(out string ValidUniqueNumber) {
        string GeneratedUniqueNumber = "";

        // Default implementation of UNIX time of the current UTC time
        TimeSpan ts = DateTime.UtcNow - new DateTime(1970, 1, 1, 0, 0, 0, 0);
        string FormatedDateTime = Convert.ToInt64(ts.TotalSeconds).ToString();
        string ssUniqueId = DateTime.UtcNow.ToString("fffffff");
        //Add Padding to UniqueId
        string FormatedUniqueId = ssUniqueId.PadLeft(7, '0'); 

        if (FormatedDateTime.Length == 10 && FormatedUniqueId.Length == 7)
        {
            // Calculate checksum number using Luhn's algorithm.
            int sum = 0;
            bool odd = true;
            string InputData = FormatedDateTime + FormatedUniqueId;
            int CheckSumNumber;

            for (int i = InputData.Length - 1; i >= 0; i--)
            {
                if (odd == true)
                {
                    int tSum = Convert.ToInt32(InputData[i].ToString()) * 2;
                    if (tSum >= 10)
                    {
                        string tData = tSum.ToString();
                        tSum = Convert.ToInt32(tData[0].ToString()) + Convert.ToInt32(tData[1].ToString());
                    }
                    sum += tSum;
                }
                else
                    sum += Convert.ToInt32(InputData[i].ToString());
                odd = !odd;
            }
            //CheckSumNumber = (((sum / 10) + 1) * 10) - sum;
            CheckSumNumber = (((sum + 9) / 10) * 10) - sum;

            // Compute Full length 18 digit UniqueNumber
            GeneratedUniqueNumber = FormatedDateTime + FormatedUniqueId + Convert.ToString(CheckSumNumber);
        }
        else
        {
            // Error
            GeneratedUniqueNumber = Convert.ToString(-1);
        }

        ValidUniqueNumber = GeneratedUniqueNumber;        
    }

**EDIT：**不能使用澄清GUID，需要通过电话键盘将号码输入IVR系统。