Harmonic Series:The harmonic series is the divergent infinite series given by $H_n = \sum_{k=1}^{n} \frac{1}{k}$.
Natural Logarithm:The natural logarithm, denoted as $\ln(x)$, is the logarithm to the base $e$, where $e$ is approximately equal to 2.71828.
Divergent Series: A divergent series is an infinite series that does not converge to a finite limit.