Earlier this year, a trio of mathematicians decided to make lemons into lemonade — and ended up making major headway on a problem that mathematicians have been thinking about for centuries.

Consider this sequence of numbers: 5, 7, 9. Can you spot the pattern? Here’s another with the same pattern: 15, 19, 23. One more: 232, 235, 238. “Three equally spaced things,” says Raghu Meka, a ...