Problem

TxO Math Bowl 2024 - Team Contest - Problem 11

How many non-empty subsets \mathcal{S} of \{1, 2, 3, 4, 5, 6, 7, 8, 9\} are there such that no element of \mathcal{S} is relatively prime to all other elements in \mathcal{S}?

Note: one element sets do not satisfy these conditions.


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Problem Tags: Counting and probability Number theory Set theory

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