证明:
由已知
$\because a_n=\frac{a^2_{n+1}}{n}+a_{n+1},$
$\therefore a_{n+1}-a_n=-\frac{a^2_{n+1}}{n}\rightarrow 0,\rightarrow a_n=a_{n+1},(n \to \infty )$
$\begin{align*}\because \lim_{n \to \infty }a_n\ln n&=\lim_{n \to \infty }\frac{a_n}{\frac{1}{\ln n}}\\\\&=\lim_{n \to \infty }\frac{a_{n+1}-a_n}{\frac{1}{\ln(n+1)}-\frac{1}{\ln n}}\\\\&=\lim_{n \to \infty }\frac{a^2_{n+1}\cdot \ln n\ln(n+1)}{n\ln(1+\frac{1}{n})}\\\\&=\lim_{n \to \infty }(a_{n+1}\ln n)(a_{n+1}\ln (n+1))\\\\&=\lim_{n \to \infty }(a_{n}\ln n)(a_{n+1}\ln (n+1)),\end{align*}$
$\displaystyle \therefore \lim_{n \to \infty }a_{n+1}\ln (n+1)=\lim_{n \to \infty }a_{n}\ln n=1.$
这里考虑到
$\displaystyle \lim_{n \to \infty }a_{n}\ln n\neq 0.$