Padovan Sequence - Binet-like Formula

Binet-like Formula

The Padovan sequence numbers can be written in terms of powers of the roots of the equation

This equation has 3 roots; one real root p (known as the plastic number) and two complex conjugate roots q and r. Given these three roots, the Padovan sequence can be expressed by a formula involving p,q and r:

where a, b and c are constants.

Since the magnitudes of the complex roots q and r are both less than 1 (and hence p is a Pisot–Vijayaraghavan number), the powers of these roots approach 0 for large n, and tends to zero.

For all, P(n) is the integer closest to, where s = p/a = 1.0453567932525329623... is the only real root of s3 − 2s2 + 23s − 23 = 0. The ratio of successive terms in the Padovan sequence approaches p, which has a value of approximately 1.324718. This constant bears the same relationship to the Padovan sequence and the Perrin sequence as the golden ratio does to the Fibonacci sequence.