Wronskian formula for confluent second-order supersymmetric quantum   mechanics
  The confluent second-order supersymmetric quantum mechanics, for which the factorization energies tend to a single value, is studied. We show that the Wronskian formula remains valid if generalized eigenfunctions are taken as seed solutions. The confluent algorithm is used to generate SUSY partners of the Coulomb potential. 
David J. Fernandez C., Encarnacion Salinas-Hernandez