Published online by Cambridge University Press: 23 January 2015
Like Fibonacci and Lucas numbers, Pell and Pell-Lucas numbers are a fertile ground for creativity and exploration. They also have interesting applications to combinatorics [1], especially to the study of lattice paths [2, 3], as we will see shortly.
Pell numbers Pn and Pell-Lucas numbers Qn are often defined recursively [4, 5]:
where n ≥ 3. They can also be defined by Binet-like formulas: