The given sequence is an arithmetic sequence where each term increases by 1.
To describe the sequence using \( n \), we can see that:
- The first term (when \( n = 1 \)) is 15.
- The second term (when \( n = 2 \)) is 16.
- The third term (when \( n = 3 \)) is 17.
- The fourth term (when \( n = 4 \)) is 18.
The general form of an arithmetic sequence is given by:
\[ a_n = a_1 + (n - 1)d \]
Where \( a_1 \) is the first term and \( d \) is the common difference. Here, \( a_1 = 15 \) and \( d = 1 \).
So, the expression for the \( n \)-th term of the sequence is:
\[ a_n = 15 + (n - 1) \cdot 1 \]
This simplifies to:
\[ a_n = 15 + n - 1 \]
\[ a_n = n + 14 \]
Therefore, the expression to describe the sequence is:
\[ a_n = n + 14 \]
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