This is an activity for upper elementary or middle school students. First, students solve puzzles, and then they make up puzzles. This video explains the basic idea, with specific page references to the worksheet:
Download the worksheet, which includes some teacher notes in the back.
Your students will also need some blank pyramids on which they can experiment.
This unit was inspired by Brad Fulton’s Pyramid Math (of which I only saw two pages.)
Many thanks to James Propp and James Tanton for valuable feedback.