The number theorist with a mystical streak. Nicomachus of Gerasa (fl. 2nd century CE) saw arithmetic not just as calculation, but as the key to cosmic harmony. His Introduction to Arithmetic became a go-to textbook for over a thousand years, blending Pythagorean number lore with philosophical purpose. He loved perfect numbers, numerical ratios, and the divine order hiding in digits. More about beauty than rigor, Nicomachus helped make math feel sacred — and surprisingly musical.