The Markov sequence problem aims at the description of possible eigenvalues of
symmetric Markov operators with some given orthonormal basis as eigenvector
decomposition. A fundamental tool for their description is the hypergroup property.
We first present the general Markov sequence problem and provide the classical
examples, most of them associated with the classical families of orthogonal
polynomials. We then concentrate on the hypergroup property, and provide a general
method to obtain it, inspired by a fundamental work of Carlen, Geronimo and Loss.
Using this technique and a few properties of diffusion operators having polynomial
eigenvectors, we then provide a simplified proof of the hypergroup property for the
Jacobi polynomials (Gasper’s theorem) on the unit interval. We finally investigate
various generalizations of this property for the family of Dirichlet laws on the
simplex.