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• (ㄱ) $\displaystyle \sum _{{n=2}} ^ {\infty} \left (\frac{n} {\ln n} \right) ^ {n}$
• (ㄴ) $\displaystyle \sum _ {n=1} ^ {\infty} \frac{2 \cdot 5 \cdot 8 \cdot \cdots \cdot (3 n-1)} {3 \cdot 7 \cdot 11 \cdot \cdots \cdot (4 n-1)}$
• (ㄷ) $\displaystyle \sum _ {n=2} ^ {\infty} \frac{1} {n \ln n}$