Prove that $\sum_{n=2}^\infty (\ln n)^{- \ln n}$ converges

As the title suggests, I'd like to prove that the sum $$ \sum_{n=2}^\infty (\ln n)^{- \ln n} $$ is finite. The root and ratio test both fail here, but WA suggests that there is a comparison that can be used to show convergence.

The only thought I have is that it may help to write the terms as $e^{-\ln(n)\ln(\ln(n))}$, but this has not led me to any particular insight. Any ideas are appreciated.


Well,

$$e^{-(\log n)(\log \log n)} = n^{-\log \log n} < n^{-2}$$

for $n > e^{e^2}$. So a comparison with $\sum \frac{1}{n^2}$ shows the convergence.


There is a theorem that for a decreasing series $\sum a_n$ converges if and only if $\sum 2^k a_{2^k}$ converges. Applying that in this case gives, where I assume the log is base $2$ just to make my life easy, $$\sum \left(\frac{2}{k}\right)^k$$ and this is easily seen to converge by root or ratio.