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• (a) $\displaystyle \sum _ {n=1} ^ {\infty} \frac{{\ln} n} {n}$ (b) $\displaystyle \sum _ {n=1} ^ {\infty} \frac{1} {n} {\sin} \left (\frac{1} {n} \right)$ (c) $\displaystyle \sum _ {n=1} ^ {\infty} \frac{1} {n} {\sin} \left (\arctan \left (\frac{1} {n} \right) \right)$