666 (number)

Since 36 is both square and triangular, 666 is the sixth number of the form <math>n^2(n^2+1)/2</math> (triangular squares) and the eighth number of the form <math>n(n+1)(n^2+n+2)/8</math> (doubly triangular numbers.)

There is no number whose value of Euler's totient function φ is 666, making it a nontotient.

The harmonic mean of the digits of 666 is an integer: 3/(1/6 + 1/6 + 1/6) = 6. 666 is the 54th number with this property.

In base 10, 666 is a palindromic number, a repdigit and a Smith number. A prime reciprocal magic square based on 1/149 in base 10 has a magic total of 666.

The Roman numeral representation of the number 666 (DCLXVI) uses once each the Roman numeral symbols with values under 1,000, and they occur in exact reverse order of their respective values (D = 500, C = 100, L = 50, X = 10, V = 5, I = 1).

[edit]

In other fields

666 is commonly known as the Number of the Beast in the Book of Revelation.

666 is also the value of the kilohertz frequency of the Bodenseesender, a big AM radio station in South Germany, which is receivable at night in all of Europe. It is also the frequency of the Australian Broadcasting Corporation's Canberra station.

In the United States, 666 is a brand name of cough syrup.

666 is the port number used by the game Doom (by id Software) when playing against another player via TCP.

In Unix and similar operating systems, a file permission of 666 (which is not uncommon) grants all users read and write permissions on the file.

Using the web coding language CSS, one may attribute a dark gray color to any web page object using the shorthand hexadecimal format: #666.

666 is the sum of all the numbers on a typical roulette wheel. (A typical roulette wheel is numbered from 1 to 36, with one (in Europe) or two (in North America) zeroes. See the point on triangular numbers, above.)