The sequence you've provided is \( 13, 26, 52, \ldots \). Observing the sequence, each term is double the previous term.
To express the sequence as an equation in terms of \( n \) (where \( n \) represents the position of the term, with \( n = 1 \) for the first term), we can identify that:
- The first term (\( n = 1 \)) is \( 13 \).
- The second term (\( n = 2 \)) is \( 26 \), which is \( 13 \times 2 \).
- The third term (\( n = 3 \)) is \( 52 \), which is \( 13 \times 2^2 \).
From this pattern, we can see that each term can be described by the formula:
\[ a_n = 13 \times 2^{n-1} \]
This means for any \( n \):
- When \( n = 1 \), \( a_1 = 13 \times 2^{0} = 13 \).
- When \( n = 2 \), \( a_2 = 13 \times 2^{1} = 26 \).
- When \( n = 3 \), \( a_3 = 13 \times 2^{2} = 52 \).
Thus the equation for the sequence is:
\[ a_n = 13 \times 2^{n-1} \]