The finite difference algorithm for higher order supersymmetry
  The higher order supersymmetric partners of the Schroedinger's Hamiltonians can be explicitly constructed by iterating a simple finite difference equation corresponding to the Baecklund transformation. The method can completely replace the Crum determinants. Its limiting, differential case offers some new operational advantages. 
B. Mielnik, L.M. Nieto, and O. Rosas-Ortiz