Ginger writes down a sequence of numbers. Each is a positive whole number from 1 to 11, and she uses each number only once. Henrietta looks at the sequence and notices that for every pair of numbers next to each other in the sequence, one is divisible by the other. What is the maximum number of numbers that Ginger wrote down?
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9 is the largest chain. Here’s one example:
(This problem is from the Math Kangaroo contest.)