‘Or the number of his name. Here is wisdom. He who has understanding let him calculate the number of the beast, for it is the number of man (or ‘of a man') and his number is six hundred and sixty six (in some manuscripts 616).'
Attempts to relate this number to emperors are unnecessary for the wild beast represents all Emperors and their Empires. Indeed by a certain level of manipulation and selection it can be made to mean almost anybody (including Caligula, Nero and Domitian).
But the number itself is significant. Six is one short of seven, the number of divine perfection, it thus represents shortfall from perfection. And six hundred and sixty six is six intensified.
There are also three sixes in a row indicating a trinity that comes short of God's perfection, and remarkably it is the sum of all the numbers that make up the square of six. In other words it hugely stresses that which comes short of God.
Furthermore in Greek letters it represents chi (six hundred) and xi (sixty) and digamma, the latter in numerical use is very similar to the sigma ending (six). Chi and final sigma represent a shortening (first and last letter) of Christos and xi bears the shape of a serpent. It may thus pictorially represent anti-Christ, a devil indwelt messiah.