\(9\) is a composite number.

\(9\) is a perfect square: \(9=3^2\).

An eneagon is a polygon of \(9\) sides.

A number is divisible by \(9\) if the sum of its digits is a number divisible by \(9\): \(4 \, 158\) is divisible by \(9\) because \(4+1+5+8=18\) and \(18\) is divisible by \(9\).

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