The following formula is involved in the calculation of factorial values:

Factorial:
where n is the nonnegative integer value for which to compute the factorial.

The following references can be used to cite this factorial calculator:
 Soper, D.S. (2014). Factorial Calculator [Software]. Available from http://www.danielsoper.com/statcalc 
 Hadamard, M.J. (1894). Sur Lâ€™Expression Du Produit 1·2·3· · · · ·(n1) Par Une Fonction Entière. Paris: Centre National de la Recherche Scientifiques. 