If the excercise says:
Let $a \in \mathbb{R}$ be an accumulation value of the real sequence $(a_{n})_{n\in\mathbb{N}}$ and an upper bound of the set $\{a_{n}\ |\ n\in\mathbb{N} \}$.
Does is mean that $a$ is also the upper bound of the real sequence $(a_{n})_{n\in\mathbb{N}}$?