5. At the vertices of a regular 9-gon (see fig.), place the numbers $2016, 2017, \ldots$, 2024, in such a way that for any three vertices forming an equilateral triangle, one of the numbers is equal to the arithmetic mean of the other two. ANSWER: place the numbers in sequence (other options are possible).

![](https://cdn.mathpix.com/cropped/2024_05_06_b74cf42a1f2649b1382dg-04.jpg?height=591&width=608&top_left_y=193&top_left_x=1318)
Solution: notice that any three numbers, spaced at equal intervals, work

   

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