@inproceedings{pedro2003every,
  title={Every positive integer is the Frobenius number of an irreducible numerical semigroup with at most four generators},
  author={Pedro A. García-Sánchez, and José C. Rosales},
  url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203611471724844},
  booktitle={Arkiv for Matematik},
  volume={42},
  number={2},
  pages={301-306},
  year={2003},
}
             
            
                
Pedro A. García-Sánchez, and José C. Rosales. Every positive integer is the Frobenius number of an irreducible numerical semigroup with at most four generators. 2003. Vol. 42. In Arkiv for Matematik. pp.301-306. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20170108203611471724844.