How many subsets of the set of divisors of $72$ contain only composite numbers? For example, $\{8,9\}$ and $\{4,8,12\}$ are two such sets. Include the empty set in your count.
Question:
How many subsets of the set of divisors of $72$ contain only composite numbers? For example, $\{8,9\}$ and $\{4,8,12\}$ are two such sets. Include the empty set in your count.
Answer:
Let's think step by step.

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512
How many subsets of the set of divisors of $72$ contain only composite numbers? For example, $\{8,9\}$ and $\{4,8,12\}$ are two such sets. Include the empty set in your count.
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