Twenty-two is the integer following 21 and preceding 23. As an even, positive whole number it appears in basic counting and arithmetic and is commonly referenced in everyday measurements and cultural contexts. For a general entry on numbers see number.
Mathematical properties
In arithmetic, 22 is composite and a semiprime: its prime factorization is 2 × 11. Its positive divisors are 1, 2, 11 and 22, a fact often summarized in divisor tables or reference works (divisors of 22). Because the sum of its proper divisors is 14 (1 + 2 + 11), 22 is classified as a deficient number. It is even, so divisible by 2; see also general notes on parity and even numbers at even number.
- Binary: 10110
- Octal: 26
- Hexadecimal: 16
- Roman numeral: XXII (Roman numerals)
Context, history and naming
The symbol "22" in modern use comes from Arabic numerals adopted in Europe during the Middle Ages, replacing older systems like Roman numerals for most calculations. In English the number is written as "twenty-two," a compound of the tens word and the unit. In geometry, a 22-sided polygon may be described informally as a 22-gon; specialized Greek-derived names exist but are rarely used in general texts.
Uses and cultural notes
Beyond mathematics, 22 appears in several familiar contexts: the chemical element titanium has atomic number 22 (symbol Ti); a cricket pitch is traditionally 22 yards long; a standard association football match features 22 players on the field at kick-off (11 per side); and some symbolic systems, such as the Tarot, recognize 22 major arcana. The number also figures in literature and popular culture — for example, the title of Joseph Heller's novel Catch-22 has become a common idiom.
Because it is small, even, and composite with only two prime factors, 22 serves as a simple illustrative example in elementary number theory and arithmetic education. For further reference on numeric concepts and notation see the general resources linked above.