It is unique. For example, consider a 5-digit number x. The sum of the digits of x represented by y will be maximum 45 (if the number x happens to be 99999). Any 2-digit number y times its reverse (which also consists of maximum 2 digits) will not yield a 5-digit number. In fact, y will consist of maximum 2 digits as long as x has maximum 11 digits. Does this make sense?