Bigger triangular numbers are also possible, though you won’t see them at the bowling alley. After 10, the next one is 1 + 2 + 3 + 4 + 5 = 15, familiar from the setup at the start of a game of pool.

These triangular snowflakes, which have three short edges and three long edges, were captured in the wild. Aerodynamics could provide a clue to their mysterious existence. Kenneth Libbrecht ...

Valkonen even thinks that some caterpillars rely on the same trick. The larvae of many swallowtails and hawkmoths react to danger by hiding their heads and flaring their abdomens into a triangular ...