Captain Hook has plundered a safe that contains 2520 gold coins. During the night, each of his pirates secretly took out some coins just for themselves. The first one took out of 1/2 the coins, the second one 1/3 of the remaining coins, the third one 1/4 of the remaining coins and so on. When Captain Hook opened the safe, he found only 252 coins inside. How many pirates were commanded by Captain Hook?