  The energy eigenvalues of the superintegrable chiral Potts model are
determined by the zeros of special polynomials which define finite
representations of Onsager's algebra. The polynomials determining the
low-sector eigenvalues have been given by Baxter in 1988. In the Z_3-case they
satisfy 4-term recursion relations and so cannot form orthogonal sequences.
However, we show that they are closely related to Jacobi polynomials and
satisfy a special "partial orthogonality" with respect to a Jacobi weight
function.
