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Find the number of ways of arranging the numbers 1, 2, 3,  9 in a circle, so that the sum of any three adjacent numbers is divisible by 3. (Two arrangements are considered the same if one arrangement can be rotated to obtain the other.)

 Oct 14, 2019
 #1
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....

 Oct 14, 2019
edited by Rom  Oct 18, 2019

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