Consider the viral magnetic clock, for example -- the one with little charms instead of numbers. It's made with an item from IKEA's kitchen section, a few other items, and some crafty creativity.

Getting a few hits with special numbers when you look at the clock can be rewarding. You may have trained your brain to look when those special numbers come up to get that small dopamine surge.

By satisfying all these properties, mathematicians can consider clock numbers with clock addition a group. In short, a group is a set with some way of combining the elements layered on top.