| ||||
|---|---|---|---|---|
| Cardinal | six hundred sixty-six | |||
| Ordinal | 666th (six hundred sixty-sixth) | |||
| Factorization | 2 × 32 × 37 | |||
| Divisors | 1, 2, 3, 6, 9, 18, 37, 74, 111, 222, 333, 666 | |||
| Greek numeral | ΧΞϚ´ | |||
| Roman numeral | DCLXVI | |||
| Greek prefix | ἑξακόσιοι ἑξήκοντα ἕξ hexakósioi hexēkonta héx | |||
| Latin prefix | sescenti sexaginta sex | |||
| Binary | 10100110102 | |||
| Ternary | 2202003 | |||
| Senary | 30306 | |||
| Octal | 12328 | |||
| Duodecimal | 47612 | |||
| Hexadecimal | 29A16 | |||
| Chinese numeral | 六百六十六 | |||
| Devanagari numeral | ६६६ | |||
666 (six hundred [and] sixty-six or triple six) is the natural number following 665 and preceding 667. It is a composite number.
In Christianity, 666 is referred to in most manuscripts of chapter 13 of the Book of Revelation of the New Testament as the "number of the beast" or "number of (a) man".
666 is the sum of the first thirty-six natural numbers, which makes it a triangular number:
666 is the largest triangular number that is also a repdigit. It is also a smith number.

In the Textus Receptus manuscripts of the New Testament, the Book of Revelation (13:17–18) cryptically asserts 666 to be "the man's number" or "the number of a man" (depending on how the text is translated) associated with the Beast, an antagonistic creature that appears briefly about two-thirds into the apocalyptic vision. Some manuscripts of the original Koine Greek, such as Editio Regia use the symbols χξϛ chi xi stigma (or χξϝ with a digamma), while later translations of the New Testament, such as Westcott and Hort, spell out the number in words.
In modern popular culture, 666 has become one of the most widely recognized symbols for the Antichrist or, alternatively Satanism. Earnest references to the number occur both among apocalypticist Christian groups and in explicitly anti-Christian subcultures. References in contemporary Western art or literature are, more likely than not, intentional references to the Beast symbolism. Such popular references are therefore too numerous to list.
It is common to see the symbolic role of the integer 666 transferred to the numerical digit sequence 6-6-6. Some people take the Satanic associations of 666 so seriously that they actively avoid things related to 666 or the digits 6-6-6. This is known as hexakosioihexekontahexaphobia.
There is a broad consensus in contemporary scholarship that the number of the beast refers to the Roman emperor Nero, who reigned from 55 to 68 AD. The Greek version of his name (Νέρων Καῖσαρ, "Neron Kaisar") transliterates into Hebrew as נרון קסר (NRON QSR), and, using gematria, yields a numerical value of 666. His Latin name, "Nero Caesar", transliterated as נרו קסר (NRO QSR), produces the number 616 instead, which is also cited as the Number of the Beast in some early biblical manuscripts.

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