You have fifteen seconds. Using standard math notation, English words, or both, name a single whole number—not an infinity—on a blank index card. Be precise enough for any reasonable modern mathematician to determine exactly what number you’ve named, by consulting only your card and, if necessary, the published literature.
Be honest (after all, nothing is at stake here except pride) and don’t read the comments (i.e. other people’s entries) until you’ve done your own. I’m abstaining from this contest so as to not risk losing. 15 seconds is up.