22 (twenty-two) is the natural number following 21 and preceding 23.
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In mathematics
22 is a semiprime, a Smith number, and an Erdős–Woods number.
22
7
=
3.14
28
…
{\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.
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. There are also 22 regular complex apeirohedra.
In culture and religion
22 is a master number in numerology.
There are 22 cards in the Major Arcana suit of a traditional tarot card deck, though they are often numbered 0-21.
In other fields
There are 22 genetically encoded amino acids throughout known life that generate proteins during RNA translation.
There are 22 of yards in a chain.
Catch-22 (1961), Joseph Heller's novel, and its 1970 film adaptation gave rise to the expression of logic "catch-22".
22 equal temperament is a popular microtonal tuning temperament due to its good approximation of harmonic intervals, especially septimal intervals.
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.
