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(fox hunting rabbits) around the 10 hole in the top of the hill, the fox wanted to eat the rabbit, the rabbit said: "you can, but must find me, I will hide in the 10 hole, you start from No. 10 to No. 1 hole, second hole, hole every 1 for every 2, third find a hole, so after class, with no limit on the number of." But the fox came and out 1000 times from morning to night, and still didn't find a rabbit. Which hole is the rabbit hidden in?