Twenty
Twenty (20) is the natural number following nineteen and preceding twenty-one. This article discusses notable facts about the number 20 and then other numbers in the twenties that lack their own article.
Twenty is a composite number, its proper divisors being 1, 2, 4, 5 and 10.
Twenty is used as a radix for vigesimal number systems.
In the old UK currency system, there were twenty shillings in a pound.
A group of twenty is often referred to as a score.
A polyhedron with twenty faces is an icosahedron.
The number 20 is used as an index in measuring visual acuity. 20/20 indicates perfect vision. When someone is able to see only after an event how things turned out, that person is often said to have had "20/20 hindsight".
Twenty is the age of majority in Japanese tradition.
See also: eighteen, nineteen, twenty, thirty, integer, list of numbers.
This article is about the number. For the year AD 20, see 20.
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Numbers in the Twenties
These sections contain facts about the number 21 through 29 for which separate articles do not exist. For the years AD 21 to AD 29, see the articles 21, 22, 23, 24, 25, 26, 27, 28 and 29.
Twenty-two is a composite number, its proper divisors being 1, 2 and 11.
Twenty-three is the ninth prime number, the sequence continues 29, 31, 37, 41,...
Twenty-four is a composite number, its proper divisors being 1, 2, 3, 4, 6, 8 and 12.
There are twenty-four hours in a day.
Twenty-five is a composite number, its proper divisors being 1 and 5.
Twenty-five is a square number.
Twenty-eight is the common name for the parrot Barnardius zonarius semitorquatus, widely distributed in Western Australia and South Australia. Its call sounds like "wenniate".
Twenty-one (21)
(Note, this article already exists)Twenty-two
Twenty-two is the natural number following twenty-one and preceding twenty-three.Twenty-three
Twenty-three (23) is the natural number following twenty-two and preceding twenty-four.Twenty-four
Twenty-four (24) is the natural number following twenty-three and preceding twenty-five.Twenty-five
Twenty-five (25) is the natural number following twenty-four and preceding twenty-six.Twenty-six
Twenty-six (26) is the number of letters in the English alphabet. In the classification of finite simple groups there are 26 sporadic groups.
Twenty-seven
Twenty-seven (27) is a cube, being 33 = 3 × 3 × 3. A 10000 day-old person is 27 years old (and some months).
Twenty-eight
Twenty-eight (28) is the second perfect number. The next perfect number is 496.Twenty-nine
Twenty-nine (29) is a prime number, being one of a pair of Twin primes.
