This is an old puzzle. I was given it in a maths lesson when I was 12. The teacher had a comb-over and died of a heart attack at 64. I would try and do the puzzle on paper, but could never get the answer right. Then computers came along ;-) It still intrigues me.
A man did a favour for a king. The king asked the man to choose his reward. The man asked for a grain of rice to be placed on the first square of a chessboard. He asked for this to be doubled on the second and all subsequent squares. How many grains of rice did he end up with?

















































