Thirty six cards to go around the class at least once. Each card is divided into two parts. There's an integer question and the answer to another card's question. One student starts with their question: "Who has..." then everyone calculated the answer and whoever has that card states "I have ..." That person continues with their question "Who has...?" and so it goes.
This activity takes my class maybe 10 minutes tops. I've played it where we set up a timer and see if they can beat their previous time or my other class' times.