666 is a hierarchy of numerals by mathematical definition. It isn't likely to change depending on which common number system you use.
http://www.m-w.com/cgi-bin/dictionary?va=hierarchy

Roman: DCLXVI
Greek: 600 60 6 (when translated)

We didn't use the Arabic system until 700+ years after Revelation was written, but if you write out the numerals as independent values (something that is taught in elementary school)

Arabic: 6*10^2 6*10^1 6*10^0

These are all by definition hierarchies. The Roman Catholic church also claims to be a hierarchy, and has since at least 100AD.  The concept of the hierarchy is an important part of Roman Catholic system, its what distinguishes a body of believers, where everyone has an equal say in the local church from the system of the antichrist, where the pope rules at the top like a dictator, and the laity (common people) have absolutely no say in the church itself.  Its the system that spawned the inquisitions, wars, and the entire system of kings/serfs that operated under the pope.

666 is suppose to contrast the 144,000 in Chapter 14.  The 666 all claim to be fathers, while the 144,000 all have the name of Jesus's Father written in their foreheads. Babylon is literally a whore of many fathers.

And as assurance that this is true, this is fundamental to what being a Christian means. Who is your father?  Are you born again?