Euler's Identity

Combine e with pi, the imaginary unit i, zero, and one in a single line: e^(iπ) + 1 = 0. This is Euler's identity, often voted the most beautiful equation in mathematics — five fundamental constants joined by three operations and nothing else.

e also hides in chance. In a coat-check mix-up among n people, the odds that nobody gets their own hat approaches 1/e (about 0.368) as n grows. The same 1/e sets the famous 37% rule for when to stop looking and choose.