Everyone agreed on the first step: Solve inside the parentheses, for 2+2=4. But after that, people split down two paths. Some multiplied first, while others divided, leading to different answers—1 and ...

For almost 200 years, Euler’s conjecture reigned in mathematics unchecked. Then, a paper came out that turned the whole thing on its head… and it did it all in just two sentences. In 1769, ...