\documentclass[a4paper]{article}

\newcommand\person[1]{\textsc{#1}}

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The sum of the natural numbers from $1$ to $n$
can be computed according to \person{Gauss}' formula:
\[
\sum_{k=1}^n k = \frac{n \cdot (n+1)}{2}
\qquad.
\]

There are more such sum formulas,
e.g. for sums of squares (\ref{squares}) and sums of cubes (\ref{cubes}):
\begin{eqnarray}
\sum_{k=1}^n k^2 &=& \frac{n\cdot(n+1)\cdot(2n+1)}{6} \label{squares} \\
\sum_{k=1}^n k^3 &=& \left(\frac{n\cdot(n+1)}{2}\right)^2 \label{cubes}
\qquad.
\end{eqnarray}

\end{document}