Definition:Lucas Number

Definition
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}$

The first few Lucas numbers are:
 * $2, 1, 3, 4, 7, 11, 18, 29, 47, 76, 123, 199, 322, 521, 843, \ldots$

Also see

 * Definition:Fibonacci Numbers