To cite the permutations package in publications use:

  Hankin, R. K. S. (2020). Introducing the permutations package.
  SoftwareX, volume 11 https://doi.org/10.1016/j.softx.2020.100453

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{Introducing the permutations package}},
    author = {{Robin K. S. Hankin}},
    journal = {SoftwareX},
    year = {2020},
    url = {https://doi.org/10.1016/j.softx.2020.100453},
  }