== Lead sentence == 

 In this earlier version of the article, I can actually understand what a perfect number is simply by reading the first sentence. In later revisions, one is confronted by an equation instead of plain English. That might be fine if the article were written for mathematicians (or even just people who are comfortable with equations), but there are the  to be considered. The topic is far enough outside my comfort zone that I'm not going to be bold and change it myself, but I'm proposing that the lead sentence should not rely on symbols, variables, or numerals to comprise a complete sentence.