222

222 is the natural number that follows 221 and precedes 223. In base-10 it is a repdigit, consisting of three identical digits. It is an even, composite number with prime factorization 2 × 3 × 37. Its divisors are 1, 2, 3, 6, 37, 74, 111, and 222. It is a Harshad number since 2+2+2 = 6 and 222 is divisible by 6 (222/6 = 37).

In numeral systems, 222 is written as CCXXII in Roman numerals; in binary it is 11011110; and in hexadecimal it is DE.

In science, 222 nanometers is a wavelength associated with far-ultraviolet ultraviolet (far-UVC) light produced by krypton chloride (KrCl) excimer lamps. This wavelength is studied for disinfection purposes because it is strongly absorbed by biological molecules and has limited penetration into human tissue, though research on safety and efficacy is ongoing.

Historically, the year 222 CE is noted in the context of the Roman Empire, when the emperor Elagabalus died and was succeeded by Severus Alexander, marking a transition in leadership during that period.

As a repdigit, 222 is often cited for its simple structure in discussions of number properties. It appears in basic arithmetic contexts and serves as an example of how a small integer can have multiple representations across numeral systems.