Show that $$ \overline \lim\limits_{n \rightarrow \infty}\left(\frac{1+a_{n+1}}{a_{n}}\right)^{n} \geq \mathrm{e} $$ For any sequence $\{a_n\}$ with positive terms, and that this estimate cannot be improved.
I found this problem in "Mathematical Analysis I" of Zorich, just Google Books and turn to page 149 of the preview. I believe this problem is somehow incorrectly stated (since I can't solve it :) ) , so I asked for sure.
Thanks.