Keypad Geometry and Divisibility of Numbers

In this article, the authors show how students can form familiar geometric figures on the calculator keypad and generate numbers that are all divisible by a common number. Students are intrigued by the results and want to know "why it works". The activities can be presented and students given an extended amount of time to think about them. As students can easily generate their own examples, they can continue to hypothesise why the property holds as the semester moves on. The proofs of the more complicated figures should be given only to those who are truly interested.