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Age 11 to 14 Short
Challenge Level

Peter wrote down a list of different positive integers less than or equal to 10.
For each pair of adjacent numbers, one of the numbers was divisible by the other. 
What is the longest list that Peter could have written?

If you liked this problem, here is an NRICH task which challenges you to use similar mathematical ideas.

This problem is taken from the UKMT Mathematical Challenges.
You can find more short problems, arranged by curriculum topic, in our short problems collection.