To cite X-13ARIMA-SEATS/seasonal in publications use:

Sax C, Eddelbuettel D (2018). “Seasonal Adjustment by X-13ARIMA-SEATS in R.” Journal of Statistical Software, 87(11), 1–17. doi: 10.18637/jss.v087.i11.

Corresponding BibTeX entry:

  @Article{,
    title = {Seasonal Adjustment by {X-13ARIMA-SEATS} in {R}},
    author = {Christoph Sax and Dirk Eddelbuettel},
    journal = {Journal of Statistical Software},
    year = {2018},
    volume = {87},
    number = {11},
    pages = {1--17},
    doi = {10.18637/jss.v087.i11},
  }