666666666

666666666 is the nine-digit decimal integer comprised entirely of the digit 6. It represents six hundred sixty-six million six hundred sixty-six thousand six hundred sixty-six and can be written as 6 × 111,111,111 or as 18 × 37,037,037. It is also two-thirds of 999,999,999, since 999,999,999 × 2/3 equals 666,666,666.

Mathematically, 666,666,666 is even and divisible by 3 and 9, as the sum of its digits (six added nine times) is 54, a multiple of 9. Consequently, it is divisible by 18 as well. The number is a repdigit, meaning it is formed by repeating the same digit in a given base (in this case, base 10).

In other bases, the representation of this value changes. For example, in base 10 it is 666,666,666, but in bases greater than 10 or in non-decimal systems, the digit sequence and length differ. As a mathematical object, it is primarily notable as an example of a large, uniform digit string rather than for a unique structural property beyond its decimal form and divisibility.

Cultural references surrounding the number 666 often relate to the Number of the Beast from Christian eschatology, which is associated with the digits 6 and 666. The specific nine-digit sequence 666666666 does not have a widely recognized distinct meaning beyond being a large repdigit.