/usr/lib/R/site-library/sandwich/CITATION is in r-cran-sandwich 2.3-4-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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citEntry(entry="Article",
         title = "Econometric Computing with HC and HAC Covariance Matrix Estimators",
         author = personList(as.person("Achim Zeileis")),
         journal      = "Journal of Statistical Software",
         year         = "2004",
	 volume       = "11",
	 number       = "10",
	 pages        = "1--17",
         url          = "http://www.jstatsoft.org/v11/i10/",
         
         textVersion = 
         paste("Achim Zeileis (2004).", 
               "Econometric Computing with HC and HAC Covariance Matrix Estimators.",
               "Journal of Statistical Software 11(10), 1-17.",
	       "URL http://www.jstatsoft.org/v11/i10/.")
)
citEntry(entry        = "Article",
         title        = "Object-Oriented Computation of Sandwich Estimators",
         author       = "Achim Zeileis", 
         journal      = "Journal of Statistical Software",
         year         = "2006",
	 volume       = "16",
	 number       = "9",
	 pages        = "1--16",
         url          = "http://www.jstatsoft.org/v16/i09/.",
         
         textVersion = 
         paste("Achim Zeileis (2006).", 
               "Object-Oriented Computation of Sandwich Estimators.",
               "Journal of Statistical Software 16(9), 1-16.",
	       "URL http://www.jstatsoft.org/v16/i09/."),
         header = "If sandwich is applied to models other than lm() also cite:"
)
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