  We consider the unital associative algebra $\mathcal{A}$ with two generators
$\mathcal{X}$, $\mathcal{Z}$ obeying the defining relation
$[\mathcal{Z},\mathcal{X}]=\mathcal{Z}^2+\Delta$. We construct irreducible
tridiagonal representations of $\mathcal{A}$. Depending on the value of the
parameter $\Delta$, these representations are associated to the Jacobi matrices
of the para-Krawtchouk, continuous Hahn, Hahn or Jacobi polynomials.
