That is 1 CE = 1 AD, and 2016 CE = 2016 AD. The word common simply means that it is based on the most frequently used calendar system: the Gregorian Calendar. Both measure the number of years before the approximate birthday of Yeshua/Jesus. Designation of a particular year in BC and BCE also have identical values.
Francium is a chemical element with symbol Fr and atomic number 87. It was formerly known as eka-caesium and actinium K. It is the second-least electronegative element, behind only caesium. Francium is a highly radioactive metal that decays into astatine, radium, and radon. As an alkali metal, it has one valence electron. Bulk francium has never been viewed.
So I guess technically Astatine and Francium is the rarest natural element on the earth that exists. Technetium and Promethium should exist but they don't, so in a sense that would make them rarer.Astatine and Francium have been produced synthetically but it is hard to do because of the short half-life.equoianoir. Apparently although there are 20 known isotopes, none of them are stable and the longest lived, astatine-210, only has a half-life of 8.3 hours.