22 (number)

22 (twenty-two) is the natural number following 21 and preceding 23.

← 21 22 23 →
← 20 21 22 23 24 25 26 27 28 29 → List of numbers Integers ← 0 10 20 30 40 50 60 70 80 90 →
Cardinal	twenty-two
Ordinal	22nd (twenty-second)
Factorization	2 × 11
Divisors	1, 2, 11, 22
Greek numeral	ΚΒ´
Roman numeral	XXII, xxii
Binary	101102
Ternary	2113
Senary	346
Octal	268
Duodecimal	1A12
Hexadecimal	1616

In mathematics

22 is a semiprime,^[1] a Smith number, and an Erdős–Woods number.^[2][3] ${\displaystyle {\frac {22}{7}}=3.14{\color {red}28}\ldots }$ is a commonly used approximation of the irrational number π, the ratio of the circumference of a circle to its diameter.

22 can read as "two twos", which is the only fixed point of John Conway's look-and-say function.^[4]

The number 22 appears prominently within sporadic groups. The Mathieu group M₂₂ is one of 26 sporadic finite simple groups, defined as the 3-transitive permutation representation on 22 points.^[5] There are also 22 regular complex apeirohedra.^[6]

22 has been proven to be a Lychrel number in base 2,^[7] since after 4 steps it reaches 10110100, after 8 steps it reaches 1011101000, after 12 steps it reaches 101111010000, and in general after 4n steps it reaches a number consisting of 10, followed by n + 1 ones, followed by 01, followed by n + 1 zeros. This number obviously cannot be a palindrome, and none of the other numbers in the sequence are palindromes.

In other fields

• Catch-22 (1961), Joseph Heller's novel, and its 1970 film adaptation gave rise to the expression of logic "catch-22".^[8]
• 22 equal temperament is a popular microtonal tuning temperament due to its good approximation of harmonic intervals, especially septimal intervals.

In culture and religion

• 22 is a master number in numerology.^[9]
• There are 22 colored properties on a traditional Monopoly board.

In weights and measures

• The number of yards in a chain.^[10]

In other uses

Twenty-two may also refer to:

• In French jargon, "22" is used as a phrase to warn of the coming of the police (typically "22, v'là les flics !", in English: "5-0! Cops!")
• In Spanish lottery and bingo, 22 is nicknamed los dos patitos, 'the two little ducks' after its shape.^[11][12]

See also

• Catch 22 (disambiguation)