BibTeX: 
@article{Stirling_FormulaAFP,
author = {Manuel Eberl},
title = {Stirling's formula},
journal = {Archive of Formal Proofs},
month = sep,
year = 2016,
note = {\url{http://isaafp.org/entries/Stirling_Formula.shtml},
Formal proof development},
ISSN = {2150914x},
}
