@profoundlynerdy You know, this is probably where we get all these stupid people asking math/puzzle questions on coding interviews—this absurd 1990s notion that skill in grade school math (not really math, more like calculation) is correlated with skill in coding. There's no valid reason to ask for Gauss' sum formula tricks to see if you can code—if there was, you might as well as about KD-trees or FFTs. If you like people who like math, fine, but don't pretend you're interviewing for coders.