Which series converges absolutely?
∑(−1)nn\sum \frac{(-1)^n}{n}∑n(−1)n
∑1n2\sum \frac{1}{n^2}∑n21
∑(−1)nn\sum \frac{(-1)^n}{\sqrt{n}}∑n(−1)n
∑−1n\sum -1^n∑−1n