Alright guys heres the answer. Its all about factors of 9. Anytime you have a number and add up its digits then subtract from the original you get a factor of 9. For example lets say you picked 99. 9+9=18. 99-18=81. If you notice, every factor of 9 (9,18,27,36 and so on) has the same symbol and they just switch the symbol that the factors of 9 have every turn.