\begin{definition}[Definition:Octagonal Number/Sequence]
The sequence of octagonal numbers, for $n \in \Z_{\ge 0}$, begins:
:$0, 1, 8, 21, 40, 65, 96, 133, 176, 225, 280, 341, \ldots$
{{OEIS|A000567}}
\end{definition}