-1 = e^iπ, — Euler's identity

"One of the most frequently mentioned equations was Eulers equation, e^{i \pi} + 1 = 0. \,\! Respondents called it "the most profound mathematical statement ever written"; "uncanny and sublime"; "filled with cosmic beauty"; and "mind-blowing". Another asked: "What could be more mystical than an imaginary number interacting with real numbers to produce nothing?" The equation contains nine basic concepts of mathematics — once and only once — in a single expression. These are: e (the base of natural logarithms); the exponent operation; π; plus (or minus, depending on how you write it); multiplication; imaginary numbers; equals; one; and zero."

"Like a Shakespearean sonnet that captures the very essence of love, or a painting that brings out the beauty of the human form that is far more than just skin deep, Eulers equation reaches down into the very depths of existence."

"There is a famous formula, perhaps the most compact and famous of all formulas — developed by Euler from a discovery of de Moivre: e^{i \pi} + 1 = 0. \,\! It appeals equally to the mystic, the scientist, the philosopher, the mathematician."

"Gentlemen, that is surely true, it is absolutely paradoxical; we cannot understand it, and we dont know what it means. But we have proved it, and therefore we know it must be the truth."