To cite the sn package in publications use:

Azzalini, A., Menardi, G., Rosolin, T. (2012). R package 'pdfCluster': Cluster analysis via nonparametric density estimation (version 1.0-0). URL http://cran.r-project.org/web/packages/pdfCluster/index.html

Corresponding BibTeX entry:

  @Manual{,
    title = {{R} package \texttt{pdfCluster}: Cluster analysis via
      nonparametric density estimation (version 1.0-0)},
    author = {A. Azzalini and G. Menardi and T. Rosolin},
    address = {Universit\`a di Padova, Italia},
    year = {2012},
    url =
      {http://cran.r-project.org/web/packages/pdfCluster/index.html},
  }