To describe the given sequence \(423, \frac{423}{5}, \frac{423}{25}, \ldots\), we can analyze the terms.
- The first term, \( a_1 = 423 \).
- The second term, \( a_2 = \frac{423}{5} \).
- The third term, \( a_3 = \frac{423}{25} \).
Notice that each term can be expressed as a fraction where the denominator is a power of \(5\):
- \(5^0 = 1\) for the first term \(423\),
- \(5^1 = 5\) for the second term,
- \(5^2 = 25\) for the third term.
From this, we can see that the \(n\)-th term can be expressed as: \[ a_n = \frac{423}{5^{n-1}} \]
Thus, the equation to describe the sequence is: \[ a_n = \frac{423}{5^{n-1}} \]