  I can't tell if you are being serious, Scott :)
If you look at that chart it seems like there are actually only a certain number of symbols even though they are listed over and over to make it look more amazing. I would suspect, the way the formula is written, that there are only a limited number of possible answers (once you add the twodigit number and subtract the sum) and if you could work out the possible answers I bet the exact same symbol is listed for all of them. And probably for each refresh of the riddle, they alternate the symbol so if you sit there in amazement, doing it over and over, you get different symbols each time so it looks like it is choosing a new one from the chart.
I am not good enough at math or riddles to figure out the numbers, but this is what occurs to me as the explanation for what is happening. Or, perhaps it's magic.

