Genus of numerical semigroups generated by three elements
  In this paper we study numerical semigroups generated by three elements. We give a characterization of pseudo-symmetric numerical semigroups. Also, we will give a simple algorithm to get all the pseudo-symmetric numerical semigroups with give Frobenius number. 
Hirokatsu Nari, Takahiro Numata and Kei-ichi Watanabe
math.GR math.AC