Since you want randomness and no duplicates, do the following. Generate a list of all consecutive numbers m to n (where m is a 15 digit number, and you may want to ignore any number that has duplicate adjacent characters, i.e. 4672950748223546). Set Count to n-m-1. Using any "good" RNG (which still could have duplicates), generate a random number x between 0 and Count, and use x as an index to select a number from the list m to n. Save the selected number in the serial number list, then remove it from the m to n list and decrement Count. Repeat n-m-1 times. Caution: This can be very slow if you have a massive list (the serial number list grows linearly - write each developed number to a file, but shrinking the massive list is slow). If you are interested, I can dig out a fast C implementation with multiple arrays that I used for randomly selecting words from a dictionary (where the list was a list of file offsets to the dictionary words). Dave.
