Moving a stack of 64 golden discs one at a time would supposedly outlast the sun
French mathematician Édouard Lucas invented and marketed the Tower of Hanoi puzzle in 1883, wrapping it in an invented legend about Hindu priests moving 64 golden discs between three posts, one at a time, never placing a larger disc on a smaller one, said to end the world when they finished. With 64 discs, the minimum number of moves is 2^64 minus 1. How many moves is that, and roughly how long would it take at one move per second?
Reveal the answer
Just over 18.4 quintillion moves. At one move per second, that's roughly 585 billion years, far longer than the current age of the universe and longer than most estimates for the sun's remaining lifespan. The puzzle's minimum-move formula, 2^n minus 1 for n discs, is a textbook example of exponential growth and recursive problem-solving still used to teach computer science today.
— Édouard Lucas, La Tour d'Hanoï — Marketed under the pseudonym 'N. Claus de Siam', 1883