My kids used to do this activity in their classes and it went something like:
Tell me all the things you know about this number.
The number would change each day and the students would brainstorm everything they knew about a number. They also used to have to provide as many questions within a specified amount of time where the answer would be the special number. Why am I telling you this? When I stumbled upon this site, it made me think of special numbers again and what a great list this is!