Notice that one symbol (the one you are thinking of) is next to 81, 72, 66, 63, 59, 45, 36, 34, 27, 22, 18, 9, and 0. I'm no mathematician, but these are clearly the only possible results of the formula.

Peski
"Marge, don’t discourage the boy! Weaseling out of something is important to learn. It’s what separates us from the animals. Except the weasel." - Homer Simpson