22 (number)

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

In mathematics

22 is a semiprime, a Smith number, and an Erdős–Woods number. $\frac{22}{7}=3.1428\dots$ is a commonly used approximation of the irrational number [[Pi|Template:Pi]], 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.

22 has been proven to be a Lychrel number in base 2, since after 4 steps it reaches 10110100, after 8 steps it reaches 1011101000, after 12 steps it reaches 101111010000, and in general after Template:Math steps it reaches a number consisting of 10, followed by Template:Math ones, followed by 01, followed by Template:Math 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".
• 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.
• There are 22 colored properties on a traditional Monopoly board.
• There are 22 cards in the Major Arcana suit of a traditional tarot card deck, though they are often numbered 0-21.

In weights and measures

• The number of yards in a chain.

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 " !", in English: "5-0! Cops!")
• In Spanish lottery and bingo, 22 is nicknamed Template:Langx after its shape.

See also

• Catch 22 (disambiguation)