The difference between O(2^n) and O(3^n) isn't trivia; if you can answer the question, then you have an understanding of what big-O means. Asking someone to recite the definition they learned of O(n) is easy; asking someone to think critically about the definition of big-O and how 2^n and 3^n relate shows a deeper understanding. I haven't memorized any trivia relating to these functions, but I convinced myself within a few seconds of the answer from the definition of big-O.
