I TA'd for Graham's Discrete math class at UCSD. He's still quite the character! His last lecture he juggled a handful of chalks in class and brought his deck of cards to do magic tricks.

He once made me pull out a 1$ bill from my pocket in his office and then asked me what the serial number was, he shot out a question like: "what's the probability that you have n consecutive numbers on the bill".

You could tell Math was legitimately fun for him, he treated open math problems like brain teasers and that fun rubbed off on the people around him as well.