Bessel polynomials

Bessel polynomials are a series of orthogonal polynomials that are related to Bessel functions, which are solutions to Bessel's differential equation. The Bessel polynomials, denoted usually by \( P_n(x) \), are defined using the formula: \[ P_n(x) = \sum_{k=0}^{n} \binom{n}{k} \frac{(-1)^k}{k!} (x/2)^k.