7, 26, 63, 124, 215, 342, ?

The answer is $\boxed{481}$.

The sequence is $a_n = 3^n – 2^n$.

Here is a brief explanation of each option:

• Option A: $391 = 3^2 \cdot 73$. This is not a term in the sequence, because $73$ is not a power of $3$.
• Option B: $421 = 3^2 \cdot 57$. This is not a term in the sequence, because $57$ is not a power of $3$.
• Option C: $481 = 3^4 \cdot 7$. This is a term in the sequence, because $7$ is a power of $3$.
• Option D: $511 = 3^3 \cdot 17$. This is not a term in the sequence, because $17$ is not a power of $3$.