\begin{definition}[Definition:Bell Number/Sequence]
The sequence of Bell numbers begins:
:$(1), 1, 2, 5, 15, 52, 203, 877, 4140, 21 \, 147, \ldots$
where the first $(1)$ is the zeroth '''Bell number''' $B_0$.
{{OEIS|A000110}}
Category:Definitions/Bell Numbers
\end{definition}