棋盘上放麦粒，为何堆满全世界？

A king once played chess with a visitor. 从前有个国王和一位客人下象棋。 The visitor asked for wheat on the board. 客人的奖品是棋盘上的麦粒。 Put one grain on the first square. 第一格放一粒麦子。 Then double it for every next square. 后面每一格都翻倍。 By the 64th square, the number is huge. 到第64格，麦子数已经是天文数字。 The king could never pay that much. 国王怎么也付不起。 Doubling grows faster than you can imagine. 翻倍的速度，比你想的还要快。