I propose a classic alignment (with align*), another (with alignat*), perhaps more pleasant to read, which consists in not repeating the sum operator on each line, and a last with a single big sum operator for the whole alignment:
\documentclass{article}
\usepackage{amsmath}
\usepackage{graphics}
\usepackage{relsize}
\newcommand\Sum{\mathlarger{\sum}}
\usepackage{lettrine}
\usepackage{showframe}
\begin{document}
\begin{align*}
& \sum_{k=1}^\infty \frac{1}{k}\rightarrow \infty &
&\sum_{k=1}^\infty \frac{1}{k^2}= \frac{\pi^2}{6}
& & \sum_{k=1}^\infty \frac{1}{k^3} = \zeta(3)
\\[1ex]
& \sum_{k=1}^\infty \frac{(-1)^{k+1}}{k}= \ln(2)
& & \sum_{k=1}^\infty \frac{(-1)^{k+1}}{k^2}= \frac{\pi^2}{12}
& & \sum_{k=1}^\infty \frac{(-1)^{k+1}}{k^3} = \frac{3}{4}\zeta(3)
\\[1ex]
& \sum_{k=1}^\infty \frac{1}{2k} \rightarrow \infty
& & \sum_{k=1}^\infty \frac{1}{{(2k)}^2} = \frac{\pi^2}{24}
& & \sum_{k=1}^\infty \frac{1}{{(2k)}^3} = \frac{1}{8}\zeta(3)
\\[1ex]
& \sum_{k=1}^\infty \frac{(-1)^{k+1}}{2k}= \frac{\ln(2)}{2}
& & \sum_{k=1}^\infty \frac{(-1)^{k+1}}{{(2k)}^2} = \frac{\pi^2}{48}
& & \sum_{k=1}^\infty \frac{(-1)^{k+1}}{{(2k)}^3} = \frac{3}{32}\zeta(3)
\\[1ex]
& \sum_{k=0}^\infty \frac{1}{2k+1}\rightarrow \infty
& & \sum_{k=0}^\infty \frac{1}{{(2k+1)}^2}= \frac{\pi^2}{8}
& & \sum_{k=0}^\infty \frac{1}{{(2k+1)}^3} = \frac{7}{8}\zeta(3)
\\[1ex]
&\sum_{k=0}^\infty \frac{(-1)^{k}}{2k+1}= \frac{\pi}{4}
& & \sum_{k=0}^\infty \frac{(-1)^{k}}{{(2k+1)}^2}\neq \frac{\pi^2}{16}
& & \sum_{k=0}^\infty \frac{(-1)^{k}}{{(2k+1)}^3} = \frac{\pi^3}{32} \neq \frac{21}{32}\zeta(3)
\end{align*}
\begin{alignat*}{3}
\mathlarger{\sum}_{k=1}^\infty \enspace & \frac{1}{k}\rightarrow \infty
& \quad \Sum_{k=1}^\infty\enspace &
\frac{1}{k^2}= \frac{\pi^2}{6}
& \quad \Sum_{k=1}^\infty\enspace & \frac{1}{k^3} = \zeta(3)
\\[1ex]
&\frac{(-1)^{k+1}}{k}= \ln(2)
& & \frac{(-1)^{k+1}}{k^2}= \frac{\pi^2}{12}
& & \frac{(-1)^{k+1}}{k^3} = \frac{3}{4}\zeta(3)
\\[1ex]
& \frac{1}{2k} \rightarrow \infty
& & \frac{1}{{(2k)}^2} = \frac{\pi^2}{24}
& & \frac{1}{{(2k)}^3} = \frac{1}{8}\zeta(3)
\\[1ex]
& \frac{(-1)^{k+1}}{2k}= \frac{\ln(2)}{2}
& & \frac{(-1)^{k+1}}{{(2k)}^2} = \frac{\pi^2}{48}
& & \frac{(-1)^{k+1}}{{(2k)}^3} = \frac{3}{32}\zeta(3)
\\[1ex]
& \frac{1}{2k+1}\rightarrow \infty
& & \frac{1}{{(2k+1)}^2}= \frac{\pi^2}{8}
& & \frac{1}{{(2k+1)}^3} = \frac{7}{8}\zeta(3)
\\[1ex]
& \frac{(-1)^{k}}{2k+1}= \frac{\pi}{4}
& & \frac{(-1)^{k}}{{(2k+1)}^2}\neq \frac{\pi^2}{16}
& & \frac{(-1)^{k}}{{(2k+1)}^3} = \frac{\pi^3}{32} \neq \frac{21}{32}\zeta(3)
\end{alignat*}
\begin{alignat*}{4}
\smash{\mathop{\raisebox{-0.7\height}{\scalebox{2.8}[4]{$ \sum $}}}_{\boldsymbol{k=}1}^{\boldsymbol\infty}}\! \enspace
& \frac{1}{k}\rightarrow \infty
& \hspace{2.5em} &
\frac{1}{k^2}= \frac{\pi^2}{6}
& \hspace{2.5em} & \frac{1}{k^3} = \zeta(3)
\\
&\frac{(-1)^{k+1}}{k}= \ln(2)
& & \frac{(-1)^{k+1}}{k^2}= \frac{\pi^2}{12}
& & \frac{(-1)^{k+1}}{k^3} = \frac{3}{4}\zeta(3)
\\[1ex]
& \frac{1}{2k} \rightarrow \infty
& & \frac{1}{{(2k)}^2} = \frac{\pi^2}{24}
& & \frac{1}{{(2k)}^3} = \frac{1}{8}\zeta(3)
\\[1ex]
& \frac{(-1)^{k+1}}{2k}= \frac{\ln(2)}{2}
& & \frac{(-1)^{k+1}}{{(2k)}^2} = \frac{\pi^2}{48}
& & \frac{(-1)^{k+1}}{{(2k)}^3} = \frac{3}{32}\zeta(3)
\\[1ex]
& \frac{1}{2k+1}\rightarrow \infty
& & \frac{1}{{(2k+1)}^2}= \frac{\pi^2}{8}
& & \frac{1}{{(2k+1)}^3} = \frac{7}{8}\zeta(3)
\\[1ex]
& \frac{(-1)^{k}}{2k+1}= \frac{\pi}{4}
& & \frac{(-1)^{k}}{{(2k+1)}^2}\neq \frac{\pi^2}{16}
& & \frac{(-1)^{k}}{{(2k+1)}^3} = \frac{\pi^3}{32} \neq \frac{21}{32}\zeta(3)
\end{alignat*}
\end{document}

