Revelation 13:18 has perhaps the most famous math problem in the whole Bible, and being a math problem it is very frequently misunderstood. It reads: “Here is wisdom. Let him who has understanding calculate the number of the beast, for it is the number of a man: His number is 666.” Now, being in Revelation and clearly a symbolic number (666 seeming to refer to the pinnacle of humanity in opposition to God, since 6 is the number of man), this number has attracted a lot of speculation with people trying to pick names that add up in Hebrew, Greek, or Roman numerals to 666.
The fact that gets missed is that Revelation clearly says that the number is calculated. Not merely that some numbers in letters (minus a few junk ones) equal 666, but that to get 666 you have to do a calculation. Most prophetic hobbyists take the 666 for granted and then go wild trying to fit a name into the number (and, to be fair, many names fit). It is an extremely rare task to see someone try to calculate 666 by some means, since its prime factorization is the rather balky 2 x 3 x 3 x 37 (which comes from the number of a man, six, times 111).
So, what set of calculations can make 666, if multiplication does not work to anything meaningful. As it happens, there is a mathematical way to calculate 666 from 8, in a way that it is very significant and fairly straightforward . First 8+7+6+5+4+3+2+1 = 36. Then 36+35+34+…+3+2+1 = 666. According to Hellenistic numerology, then, 8 = 36 = 666. Coincidentally, 36 equals 6 squared, keeping the connection of the “perfect human rebellion against God” theme alive that 666 also possesses.
What is the significance of 8 insofar as it relates to 666? Here we enter the deep waters of both pagan Hellenistic theology as well as early Roman history. According to the Hellenistic theology that became gnostic Christianity (a good example of which can be found in Gary North’s Economic Commentary on the Book of Genesis), the seventh day creation (and its Sabbath) was defective because it points to the earthly creation (and sin and the fallen state of man) and so therefore to redeem creation one must worship on the eighth day, which coincidentally happens to be the first day of the week. Shades of this sort of inane reasoning can be found in the Beatles song “Eight Days A Week,” perhaps coincidentally.
So we see that the bogus religious worldview of the Hellenistic period considered 8 as a particularly important number, being above and beyond the seven day week. And, it ought to be fair, the Bible itself contains such a distinction as the eighth day, after the seven day Feast of Tabernacles, symbolizes the “eighth day” of creation when sin will be removed and the new heavens and new earth and the New Jerusalem will come down from heaven and God will make his throne in a never-ending rule without darkness or night or sin. That is in the future, a time we have not yet reached. This is why there remains a seventh-day Sabbath rest for the people of God  , because we are still in history and still looking forward to the seventh day “rest” of the Millennial kingdom, and therefore still subject to the seven day creation week and its typology. What Hellenistic thought tried to do is tried to claim that we were already beyond the creation and the laws of the Creator by virtue of some mystical knowledge (including Hellenistic numerical thinking), claims that have been repeated by Gnostic Hellenistic “Christians” to this day.
The second bit of relevance concerns Roman history. Revelation speaks of an eighth beast that is part of the seven and yet has its own identity. The meaning of this particular beast seems to suggest the eighth Roman emperor in a list (if one uses the Preterist meaning), which would be Domitian, or an end-time revival of the Roman Empire (I personally believe both meanings are valid). In the case of both Domitian and the end-time revival of the Roman Empire there is a connection between the number 8 and the divine ruler cult by which pagan rulers considered themselves to be divine manifestations of some deity, whether that means a vicar of Christ or an emanation of Jupiter or whatever other deity such heathen idolaters believe(d).
What we see is that by paying attention to the calculation of numbers, we can a greater understanding about the meaning and identity of the enemy of biblical Christianity and the reasons for that hostility in the opposition of Babylonian religion and its offshoots to the biblical God of Creation and His laws, including the Sabbath and the restrictions on the power and authority of rulers (see Deuteronomy 17:14-20). Those leaders who want to consider themselves as more than mere viceroys of God will always show hostility to the divine egalitarian order by which all men, women, and children are created in the image and likeness of God and deserving of respect and honor accordingly. That mindset is something that the Hellenists and their prototypical tyrannical god-kings simply cannot understand or accept. Let us make sure we are not among such company ourselves.