2. (2nd Quiz, 2nd Question, provided by Huang Yumin) Given a sequence of positive numbers $a_{1}, a_{2}, a_{3}, \cdots$, satisfying $a_{n+1}$ $=\frac{1}{a_{1}+a_{2}+\cdots+a_{n}}(n \in N)$. Find $\lim _{n \rightarrow \infty} \sqrt{n} a_{n}$.