Provide starting value, then remove numbers from that value, then list what values are rem

Is it possible to have excel keep a "tally" of numbers being used, based on information provided by the user?

Example:

• User enters in 300 as the starting point. (Maybe into a form field or whatever)

• Then, once that total number is set, the user then enters in unique numbers to remove from that total.

• The program or formula would then spit out how many total "numbers" are left, but also be able to say which "numbers" haven't been used yet.

A Visual Example:
I choose 250 as my starting total.
I then type in 2, 15, 35, 99, 102.
That means that I have 245 total numbers left to use, and of those 245, only the numbers that have not been selected can be used for the next round of numbers being chosen. Basically, anything but 2, 15, 35, 99 & 102 can be selected next out the remaining 245 numbers.

This "number selection" process would continue until all 250 numbers have been used up. At which point, the project would be complete. This whole process in the real world could take weeks, months, or even a year or more to complete.

I would need the ability to tell how many total numbers are left (the easy part), and then also have the ability to list exactly what numbers haven't been used yet (the hard part! (for me)).

Is this possible? I'm sure that it is but I have no idea where to begin.
Maybe excel isn't even the right choice for this. Maybe PHP? Maybe something else?

This site has always been of great help to me in the past. I'm hoping that I can get some feedback/guidance on this conundrum that I'm asking about now.

Thank you in advance to whichever genius out there is able to guide me.

-Mike in CA

There are different ways it could be done. I used a listbox form control in the attached file.