To cite symmoments in publications use:

Kem Phillips (2010). R Functions to Symbolically Compute the Central Moments of the Multivariate Normal Distribution. Journal of Statistical Software, Code Snippets, Forthcoming.

Corresponding BibTeX entry:

  @Article{,
    title = {{R} Functions to Symbolically Compute the Central Moments
      of the Multivariate Normal Distribution},
    author = {Kem Phillips},
    journal = {Journal of Statistical Software, Code Snippets},
    year = {2010},
    note = {Forthcoming},
  }