Chess Doubling

... that tells of a not-so-wise king who was tricked by a merchant. In exchange for creating the game of chess, the merchant asked for a simple reward in return.  One piece of rice placed on the first square of a chess board.  Then double this on the second square. Double again on the third, etc. By the time you get to the 64th square, there is not enough rice in the world to pay this debt...  Thus, I won't be asking about that!  However, what about the 16th square?  How much rice would be balancing in the 16th square?  

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