GB Caird (Revelation of Saint John, 174-176) offers a neat summary of the options for interpreting the mark. The number appears to be a gematria, a numerical value given to a name, popular in the first century. It is the numerical value of the name “Neron Caesar,” but only if the emperor’s name is first transliterated into Hebrew. The Greek spelling totals 1005, not 666. Greek gematria typically have higher values than Hebrew. Titus is 880, Sabastos 978. 

He cites Stanislas Giet’s theory that 666 is the total of the first letters of the names of Roman emperors from Caesar to Vespasian, but “this result . . . is attained by the curious and not obviously justifiable means of including Galba, but omitting Otho and Vitellius” (Caird 1966: 175). Stauffer argues that the total comes from an abbreviation of the Greek translation of Domitian’s title, “Autokrator Kaisar Dometianos Sebastos Germikos,” A.KAI.DOMET.SEB.GE. Portions of this title appear on coins from the period, but “there is no single coin on which all five occur together” (175). Besides, on my interpretation, a reference to Domitian is out of time in any case.

Caird raises the critical point: John “would not have used gematria at all unless the number 666 had appealed to him for other symbolic reasons.” What might those reasons be?

Caird writes, “666 is a remarkable number in many ways. It is the number which persistently falls short of the perfect number 7, It is the parody of the number of Jesus, 888; six being the number of Good Friday and eight the number of Easter Day. It is two-thirds of a thousand, one third of the monster’s kingdom having been destroyed by the trumpet plagues. Above all it is a triangular number, in sinister contrast with the square numbers of the martyrs and the heavenly city. . . . The sum of a series of consecutive numbers beginning with unity n(n+1)/2 was a triangular number; and 666 is the triangular of 36, which is the triangular number of 8 – and the monster is an eighth (xvii.11)” (176).

If triples are sinister as compared to squares, 666 is double sinister, being the triangulation of 36, which is itself a triple of the number of Israel, 3 x 12.