April 15, 2019
A friend of mine (whose last name is Songer) recently mentioned an unusual observation at a dinner party—if one subtracts a number from its reversal, the result is always divisible by nine. In a textbook example of nerd sniping, I and a couple of other friends whipped out calculators to convince ourselves and spent a few minutes trying to find a proof (as one does at dinner parties). Not all of the guests that night were fond of math, so we set the problem aside when the proof wasn't immediately forthcoming. However, an unresolved sense of mathematical angst propelled me toward a proof the next day, and it has an interesting consequence.Read more...