Bessel polynomials

Summary

The Bessel polynomials $y_n$ are polynomials with positive integer coefficients that arise from the modified Bessel functions of half-integer order. They solve a second-order differential equation with polynomial coefficients. They are orthogonal for a weight on a circle in the complex plane, not on an interval of the real line. Their reversed forms are the denominators of Bessel filters in electrical engineering.