Chi Xi Digamma, like Iota Eta Sigma, is NOT a fraternity. It is rather the Greek alphanumeric for 600 + 60 + 6 = 666, the number of the Beast. In Hebrew it would have been msw (mem samedh waw).
" "Wisdom is needed here; one who understands can calculate the number of the beast, for it is a number that stands for a person. His number is six hundred and sixty-six." (Revelation 13:8)
Because it comes from the bottomless pit (9:1ff.) it is inspired by Satan, whom it represents on earth. It is the Antichrist, who musters and marshals the enemies of the two witnesses. (Jerome Bibilical Commentary 54:7) The investiture of the Beast is opposed to the enthronement of the Lamb (5:12). The dragon, the prince of this world, presumes to claim temporal powers (Lk 4:6f.) of which God is the one true custodian (Jn 19:11; Rom 13:1). (JBC 62:2) The best attested number in the mss. is 666; but some ancient texts read 616. The key to this numerological message was lost very early, even before Irenaeus? time. Since then many hypotheses (some of them extravagant) have been proposed. The solution is to be found in gematria, for it is a question of "the number of a man," i.e., a number equivalent to the sum of the letters in a man's name. The most widely accepted theory identifies 666 with Neron Caesar, written NRWN QSR in Hebrew (= 50 + 200 + 6 + 50 + 100 + 60 + 200; see D. R. Hillers, BASOR 170  65). The Latin form of the name (without the final N of NRWN) would equal 616, the alternative reading of the manuscripts. Nero fits the context, for he was the first emperor to persecute the Christians; he embodied all the worst characteristics of the Beast, and he came to life again in Domitian. Another possible interpretation is that of the 'triangular number': 666 is the sum of all numbers from 1 to 36; 36 is the sum of all numbers from 1 to 8; 8 would then be the number designating Nero redivivus (17:11) (JBC 63:18)
Interestingly 666 is a triangular number, the sum of the first 36 integers and also the sum of the squares of the first six primes, a Smith number (whose factors' digital root equals its own) and a homodigital.
"Anyone who worships the beast or its image, or accepts its mark on forehead or hand, will also drink the wine of God's fury, poured full strength into the cup of His wrath, and will be tormented in burning sulfur before the holy angels and before the Lamb. The smoke of the fire that torments them will rise forever and ever, and there will be no relief day or night for those who worship the beast or its image or accept the mark of its name." (14:9-11)
"On the sea of glass were standing those who had won the victory over the beast and its image and the number that signified its name." (14:19)
""The first angel went and poured out his bowl on the earth. Festering and ugly sores broke out on those who had the mark of the beast or worshiped its image." (15:8)
The fifth angel poured out his bowl on the throne of the beast. Its kingdom was plunged into darkness, and people bit their tongues in pain and blasphemed the God of heaven because of their pains and sores. But they did not repent of their works." (16:6)
"I saw three unclean spirits like frogs come from the mouth of the dragon, from the mouth of the beast, and from the mouth of the false prophet. These were demonic spirits who performed signs. They went out to the kings of the whole world to assemble them for the battle on the great day of God the almighty." (16:13-14)
"Then I saw the beast and the kings of the earth and their armies gathered to fight against the one riding the horse and against his army. The beast was caught and with it the false prophet who had performed in its sight the signs by which he led astray those who had accepted the mark of the beast and those who had worshiped its image. The two were thrown alive into the fiery pool burning with sulfur." (19:19-20)
"The Devil who had led them astray was thrown into the pool of fire and sulfur, where the beast and the false prophet were. There they will be tormented day and night forever and ever." (20:10)