15: That’s the answer to an incredibly complicated math problem recently solved by a two-person team at Carnegie Mellon University (CMU). Usually, big, complicated math problems that are hard to solve have big, complicated answers that are almost equally hard for the layperson to understand. But not this one. This one is just … 15.
The question, originally posed in 2008, went as such: If you had an infinite grid of squares—like a sheet of graph paper that went on for eternity—and you wanted to fill it with numbers that had to be more- than- that-number squares apart, what is the minimum number of different numbers you would need? This is called the “packing coloring” problem.