It could be far more simpler than all that.
The Bible warns us not to add to or take away from scripture in all three major divisions of the Bible.
Deuteronomy 4:2 (NASB95)
2 “You shall not add to the word which I am commanding you, nor take away from it, that you may keep the commandments of the Lord your God which I command you.
Revelation 22:18-19 (NASB95)
18 I testify to everyone who hears the words of the prophecy of this book: if anyone adds to them, God will add to him the plagues which are written in this book;
19 and if anyone takes away from the words of the book of this prophecy, God will take away his part from the tree of life and from the holy city, which are written in this book.
Proverbs 30:5-6 (NASB95)
5 Every word of God is tested; He is a shield to those who take refuge in Him.
6 Do not add to His words Or He will reprove you, and you will be proved a liar.
Dr. Chuck Missler teaches that the book of Revelation is a good book to begin with in learning the Bible because all the puzzling imagery and symbolism and numbers are defined elsewhere in the Bible.
Taking all these into consideration...
666 appears only 4 times in the entire Bible.
The one we are most familiar with:
Revelation 13:18 (NASB95)
18 Here is wisdom. Let him who has understanding calculate the number of the beast, for the number is that of a man; and his number is six hundred and sixty-six.
This is also a prophetic sign post with more hints / clues in it than appears on the surface (once you realize what you are looking at).
But first, let's take a look at the other verses.
Ezra 2:13 (NASB95)
13 the sons of Adonikam, 666;
For those who would take this as a genealogical sign (to trace the lineage of the beast through this line) there is a second census that took place where there was an addition to the clan in the biblical record:
Nehemiah 7:18 (NASB95)
18 the sons of Adonikam, 667;
It is doubtful at best that this is the genealogical line of the beast (who will be / is Jewish, btw).
So what can we glean from Ezra 2:13?
The name Adonikam (in Hebrew: adonai qum meaning "risen lord") is on the one hand a prophetic reference to the risen LORD our Savior Jesus Christ. But as we know the devil is a copy cat and mimics God so as to appear to be God to confuse and confound as many as possible. That, and the word "lord" is not exclusively applied to God even in the Bible (see 1 Peter 3:6 for example). It can mean simply one who is in power... So "risen lord" can be a prophetic reference to:
Revelation 13:3 (NASB95)
3 I saw one of his heads as if it had been slain, and his fatal wound was healed. And the whole earth was amazed and followed after the beast;
I have heard superstitious preachers who do not believe anyone but God can do miracles claim this was just a faked resurrection. But there is nothing in scripture that says God alone can do miracles. See Deuteronomy 13:1-5 speaks of the signs (miracles) coming to pass. So we should not be fooled by the presence of miracles but rather be discerning of who the miracles point to and what they affirm and the only way to do that is with scripture (1 Thessalonians 5:21, 1 John 4:1, Acts 17:11, 2 Timothy 3:16-17, John 16:13, 2 Peter 1:20-21)
This resurrection will convince everyone who is not filled with the Holy Spirit (Matthew 24:24) that he is who and what he says he is (2 Thessalonians 2:3-4). Jesus even warned the Jewish people:
John 5:43 (NASB95)
43 “I have come in My Father’s name, and you do not receive Me; if another comes in his own name, you will receive him.
The word "if" is the word "ean" in Greek which would be better translated "though."
43 “I have come in My Father’s name, and you do not receive Me; THOUGH another comes in his own name, you will receive him.
This is why Jesus did not go around making pronouncements about being God incarnate. He came in his Father's name not his own. But the beast will be tooting his own horn (as we used to say) in 2 Thessalonians, Daniel, Revelation claiming to be God above all gods.
The other two verses are:
1 Kings 10:14 (NASB95)
14 Now the weight of gold which came in to Solomon in one year was 666 talents of gold,
2 Chronicles 9:13 (NASB95)
13 Now the weight of gold which came to Solomon in one year was 666 talents of gold,
As with many entries Kings and Chronicles often repeat each other... but this is a unique sign (post) in Revelation 13:18 and for 2 of the only 4 uses of 666 in the Bible it must be intended for us to take notice of.
Solomon, a man who God loved (Jedidiah) and who was so humble in the beginning as to ask only for wisdom to lead the people was given that wisdom and all that he did not ask for because he so pleased God... did not have the Holy Spirit indwelling him (which no man did until after the cross of Christ). Solomon did not take his own advice to heart and married foreign women (some for peace treaties, but most for his lusts) and he built temples to their gods in the Holy Land. Needless to say the end of his life was not like the early part. God was even willing to split the kingdom from Solomon... except that God honored Solomon's father David by not splitting it until Solomon's son took the throne.
More as time allows.