20  

Cardinal  twenty 
Ordinal  20th (twentieth) 
Numeral system  vigesimal 
Factorization  
Divisors  1, 2, 4, 5, 10, 20 
Roman numeral  XX 
Binary  10100_{2} 
Octal  24_{8} 
Duodecimal  18_{12} 
Hexadecimal  14_{16} 
20 (twenty) is the natural number following 19 and preceding 21. A group of twenty units may also be referred to as a score.^{[1]}
Contents 
Twenty is the third composite number comprising the product of a squared prime and a prime. It is the second composite number of the form p^{2}q; a squareprime, and also the second member of the (2^{2})q family in this form. 20 has an aliquot sum of 22 (110% in abundance). Accordingly, 20 is the third abundant number and demonstrates an 8 member aliquot sequence; {20,22,14,10,8,7,1,0} 20 is the 4th composite number in the 7aliquot tree. Two numbers have 20 as their aliquot sum; the discrete semiprime 34 and the squared prime 361. Only 2 other square primes are abundant 12 and 18.
20 is:
20 A.D., 20 B.C., 1920, 2020, etc.
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Order  twentieth 

Twenty is the number that is after nineteen and before twentyone.
The prime factors of twenty are 2, 2, and 5. (2 * 2 * 5 = 20)
Its factors are: 1, 2, 4, 5 and 10. As the sum of its factors is more than itself (ie 22), it can be referred to as an abundant number.
20 can been used as a number base. Remnants of this system remain in some European languages, for example in the English “score” (20) and the French “quatre vingts” (80, literally four groups of twenty). The old (predecimal) English monetary system enjoyed twenty shillings in a pound. The ancient Mayan numerical system  counting on fingers and toes  was a base 20 or "vigesimal" system.
A polyhedron of 20 faces is an icosahedron: one of the five Platonic solids. It is a convex regular polyhedron composed of twenty triangular faces, with five meeting at each of the twelve vertices. It has 30 edges and 12 vertices. Its dual polyhedron is the dodecahedron.
In Japanese tradition, adulthood is established at the age of 20. See seijin not hi (the celebration of the adulthood in Japan).
It is the number of milk teeth in a infant’s mouth.
