\begin{definition}[Definition:Pell-Lucas Numbers]
The '''Pell-Lucas numbers''' are a sequence $\left \langle {Q_n}\right \rangle$ which is formally defined by the recurrence relation:
:$Q_n = \begin{cases} 2 & : n = 0 \\
2 & : n = 1 \\
2 Q_{n - 1} + Q_{n - 2} & : \text {otherwise}\end{cases}$
The sequence of '''Pell-Lucas numbers''' begins:
:$2, 2, 6, 14, 34, 82, 198, 478, 1154, \ldots$
{{OEIS|A002203}}
\end{definition}