Definition:Lucas Number

The Lucas numbers are a sequence which is formally defined recursively as:


 * $$L_0 = 2; L_1 = 1; L_n = L_{n-1} + L_{n-2}$$.

Compare the Fibonacci numbers.

We can see that the first few Lucas numbers are:


 * $$2, 1, 3, 4, 7, 11, 18, 29, 47, 76, 123, 199, 322, 521, 843, \ldots$$