In the attached workbook, a UDF was coded to generate a numerical value, based upon a character string. Part 2 would actually be the reverse. If one has a numerical value, then what random 16 character hexadecimal string would = a numeric value. This doesn't have to be directly related to the values generated within the UDF, in fact, it shouldn't be. The reason for wanting a random 16 character hexadecimal string is that any number of 16 character strings could equal a particular value.
If there is numerical value that equals 65, then that value would translate into any number of 16 digit Hexadecimal characters (0-F). The 16 digit string 80201BA30A910532 equals the number 65. But, as can be seen, any number of characters could have been used to satisfy the 65 value...that's why a random 16 digit string that equals a particular number is desired.