\begin{definition}[Definition:Pentagonal Number/Sequence]
The sequence of pentagonal numbers, for $n \in \Z_{\ge 0}$, begins:
:$0, 1, 5, 12, 22, 35, 51, 70, 92, 117, 145, 176, \ldots$
{{OEIS|A000326}}
\end{definition}