666 is the sum of the first 36 natural numbers (i.e. 1 + 2 + 3+ ... + 34 + 35 + 36 = 666), and thus it is a triangular number. Notice that 36 = 15 + 21; 15 and 21 are also triangular numbers; and 152 + 212 = 225 + 441 = 666.
In modern popular culture, 666 has become one of the most widely recognized symbols for the Antichrist or, alternatively, the Devil. The number 666 is reportedly used to invoke Satan. Earnest references to the number occur both among apocalypticistChristian 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 not uncommon to see the symbolic role of the integer 666 transferred to the 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.
In some early biblical manuscripts, the number is cited as 616.
In the Bible, there may be a latent reference to 666 in the name of the great sixth-century BC king of Babylon. Commonly spelled Nebuchadnezzar, transliterating from the book of Daniel, the name is Nebuchadrezzar or Nebuchadrezzur in the book of Jeremiah (see Jeremiah 49:28–30). The number of each name can be calculated, since Hebrew letters double as numbers (see Hebrew numerals). Nebuchadrezzar is 663, and Nebuchadrezzur, 669. Midway between the two variants is 666. If the mysteries of Jeremiah are to be related to those of Revelation, Nebuchadrezzar, who came (though bidden by God) to crush God’s people, may prefigure the end-times beast.
Using the same system in Hebrew of generating a number from the letters of a name, Neron Caesar written in Hebrew produces the number 666. Thus, in the Bible, 666 may have been a coded reference to Nero the Roman Emperor from 55 to 68 AD.
In Kabbalistic Judaism, 666 is the number which represents the creation and perfection of the world. The world was created in 6 days, and there are 6 cardinal directions (North, South, East, West, Up, Down).