Fuente TeX:

\frac{a_{n+1}}{a_n} = \frac{n+1}{n} \frac{\lambda^{n+1}}{\lambda^{n}}\frac{e^{-\sqrt{n+1}}}{e^{-\sqrt{n}}}=\left(1+\frac{1}{n}\right) \lambda \frac{1}{e^{\sqrt{n+1}-\sqrt{n}}}