Puzzles
Double the Grain on Every Chessboard Square
A ruler offers to reward the inventor of chess with wheat: one grain on the board's first square, two on the second, four on the third, doubling all the way to the 64th square. It sounds like a modest, almost stingy prize. Before agreeing, how much wheat is the ruler actually promising to hand over?
Reveal the answer
The total comes to 2^64 minus 1 = 18,446,744,073,709,551,615 grains — a mountain of wheat larger than everything humanity has ever harvested. The legend was already being recorded by 1256, by the historian Ibn Khallikan, and it remains a classic demonstration of how fast doubling outruns intuition.