\begin{definition}[Definition:Lucas Number/Definition 1]
The '''Lucas numbers''' are a sequence which is formally defined recursively as:
:$L_n = \begin{cases}
2 & : n = 0 \\
1 & : n = 1 \\
L_{n - 1} + L_{n - 2} & : \text{otherwise} \end{cases}$
\end{definition}