# 22 (number)

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

 ← 21 22 23 →
Cardinaltwenty-two
Ordinal22nd
(twenty-second)
Factorization2 × 11
Divisors1, 2, 11, 22
Greek numeralΚΒ´
Roman numeralXXII
Binary101102
Ternary2113
Octal268
Duodecimal1A12

## In mathematics

The first 22 numbers can be arranged on a graph such that select sums between two numbers in the set yield all primes from 3 to 43. The graph has near-perfect vertical and horizontal reflective symmetry.

22 is an even composite number and the eighth semiprime; its proper divisors are 1, 2, and 11.

22 is:

Furthermore,

• 22 divided by 7 is a commonly used approximation of the irrational number π, the ratio of the circumference of a circle to its diameter. They are also consecutive hexagonal pyramidal numbers.
• 22 can read as "two twos," which is the only fixed point of John Conway's look-and-say function.
• There are 22 regular complex apeirohedra, of the form p{a}q{b}r: 8 are self-dual, while 14 exist as dual polytope pairs. 21 belong in $\mathbb {C} ^{2}$  while one belongs in $\mathbb {C} ^{3}$ . 
• There is a set of 22 single-orbit convex tilings that tessellate two dimensional space with face-transitive, edge-transitive, and/or vertex-transitive properties: 11 are regular and semiregular (or Archimedean), and 11 are dual to these, known as Laves tilings.
• There are 22 edge-to-edge star polygon tilings in the second dimension that incorporate regular convex polygons. 18 involve specific angles, while 4 involve angles that are adjustable.

## In aircraft

• 22 is the designation of the USAF stealth fighter, the F-22 Raptor.

## In sports

• In both American football and association football, a total of 22 players (counting both teams) start the game, and this is also the maximum number of players that can be legally involved in play at any given time.
• In Australian rules football, each team is allowed a squad of 22 players (18 on the field and 4 interchanges).
• The length of a cricket pitch is 22 yards.
• In rugby union, the "22" is a line in each half of the field which is 22 meters from the respective try line. It has significance in a number of laws particularly relating to kicking the ball away.
• A snooker game (called a "frame") starts with 22 coloured balls at specified locations on the table (15 red balls and 7 others).

## In other uses

Twenty-two may also refer to: