# Inspired by Archit Boobna

**Calculus**Level 4

For every real number \( z \), define the infinite nested logarithm as the limit of the series

\[ a_1 = \ln z \\ a_ 2 = \ln_{ \ln z } z \\ a_3 = \ln_{ \ln _{ \ln z } z } z \\ \vdots \]

where \( a_{n+1} = \ln_{a_n} z \).

For what value of \(Z\), does the limit of the sequence \( a_n \) exist for all \( z > Z \)?