667

667 is the natural number that comes after 666 and before 668. In mathematics it is an odd composite number with prime factorization 23 × 29, making it a semiprime.

In Roman numerals, 667 is written as DCLXVII.

It is not a prime, a square, or a cube, and it does not belong to any widely referenced named sequences with notable properties.

In physics, 667 nanometers lies in the red region of the visible spectrum.

In popular culture, 666 is more famous as the "number of the beast"; 667 is sometimes mentioned because of its proximity but has no canonical significance.

In the United States, 667 is an overlay area code for the Baltimore area, used alongside 410 and 443.