22
From Halbeeg, the open encyclopedia · Af-Soomaali
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22 is a natural number between 21 and 23. It is an even number, as it is divisible by two without remainder. In the decimal system it is written as two twos.
22 has wide daily use: it is the legal age of majority in many countries, it appears in team and player numbers, and it occurs in various historical and measurement contexts. Its mathematical properties derive from its divisors: 1, 2, 11, and 22.
Mathematical properties
22 is a composite number, as it has divisors other than 1 and itself. Its prime factorization is 2 × 11, making it a semiprime—the product of two primes. The sum of its proper divisors (1 + 2 + 11) is 14, which is less than 22, so it is a deficient number.
22 is also the second pentagonal number of a certain type and is among numbers listed as centered heptagonal. In practical mathematics, the fraction 22/7 is a classical approximation for pi (π), with a value of approximately 3.142857.
Notation and representation
In Roman numerals, 22 is written as XXII. In binary (base 2) it is 10110. In Arabic numerals it is written ٢٢. The Hebrew alphabet contains 22 basic letters, a fact that holds particular cultural and religious significance in Jewish tradition.
General usage
In the calendar, the 22nd falls in every month. Historically, years ending in 22 are commonly abbreviated. In sports, a complete football team has 22 players on the field (11 on each side). The Major Arcana of tarot cards comprises 22 cards.