Mathematics

Problem

Which of the following series is divergent? a)

\displaystyle \sum_{n=2}^{\infty} \frac{(-1)^{n}}{n\ln n}

\displaystyle \sum_{n=1}^{\infty} \frac{1}{\sqrt n}

\displaystyle \sum_{n=1}^{\infty} \frac{2^{n}}{n!}

\displaystyle \sum_{n=1}^{\infty} \frac{(-1)^{n}}{\sqrt n}