Suppose f: R →(0, ∞) be a differentiable function such that 5 f(x+y)=f(x) · f(y), ∀ x, y ∈ R. If f(3)=320, then Σ_n =0^5 f( n ) is equal to:

Suppose $\displaystyle f: \mathbb{R} \rightarrow(0, \infty)$ be a differentiable function such that $\displaystyle 5 f(x+y)=f(x) \cdot f(y), \forall x, y \in \mathbb{R}$. If $\displaystyle f(3)=320$, then $\displaystyle \sum_{\mathrm{n}=0}^5 f(\mathrm{n})$ is equal to :