the answer 1002 might actually be performed.
i only just tested myself with simple 1 and 2 and 3 combination, which starts at 111, and find the largest possible number which starts from 11, which is 113, and so on and so on, with exception of getting other duplicate starting number (starts with 22, or 33); before using the largest possible number, fill it first with the same numbers, then after 222 or 333 removed, continued as before
the result of combination using 123 should be like this:
therefore, with some computing algorithm and decent database to store and validate inputted combination to avoid duplicates, it might works. i havent tested with 10 numbers combinations though, i will try to write the algorithm and test with 10 numbers later