The reproduction of a certain bacterium doubles every hour, and the number increases to 10.24 million after 10 hours. When the number of bacteria increases to 2.56 million, how many hours does it take?
某细菌繁殖每小时增加1倍，10小时后增加到1024万个，当细菌增加到256万个时，用了多少小时．
<result>8</result>