One grain of rice, doubled 63 times, bankrupts an empire

In the old legend, a sage asks a king for one grain on the first chessboard square, two on the second, doubling each time. The final total — 2^64 minus 1 — is about 18 quintillion grains, more rice than the world has ever grown. Human intuition is linear; compounding is not.

— Traditional; Ibn Khallikan, The wheat and chessboard problem (attested in Ibn Khallikan's biographical dictionary) — c. 1256