Let \( f(x) \) be a function such that \( f(x+y) = f(x)\cdot f(y) \) for all \( x, y \in \mathbb{N} \). If \( f(1) = 3 \) and \( \displaystyle \sum_{k=1}^{n} f(k) = 3279 \), then the value of \( n \) is:
\( 6 \)
\( 7 \)
\( 8 \)
\( 9 \)