Number reference
20 explained.
20: twenty, composite; factors, prime factorization, roots, binary, hexadecimal, and digit properties.
Identity and representations
- Written form
- twenty
- Classification
- composite
- Factors
- 1, 2, 4, 5, 10, 20
- Prime factorization
- 2 × 2 × 5
- Square root
- 4.472136
- Cube root
- 2.714418
- Binary
- 10100
- Octal
- 24
- Hexadecimal
- 14
- Roman numeral
- XX
- Digit sum
- 2
- Digital root
- 2
What makes 20 notable
- Factor structure. 20 breaks down into 2 distinct primes (2, 5) and has 6 divisors in total, so it can be split into equal whole-number groups 4 ways beyond 1 and itself.
20 in everyday use
Twenty is the atomic number of calcium and the count of fingers and toes together, which is why several languages count in twenties: French says quatre-vingts, "four twenties", for 80, and Lincoln's "four score and seven" means 87. Normal eyesight is 20/20, meaning you read at twenty feet what a standard eye reads at twenty feet. The twenty-sided die of tabletop games is an icosahedron, one of the five Platonic solids. Twenty Questions is the classic guessing game.
Twenty is the third tetrahedral number, 1 + 3 + 6 + 10, the number of balls in a triangular pyramid four layers high. It is abundant, since its proper divisors 1, 2, 4, 5, and 10 add to 22. It has six divisors and is the smallest number with exactly that many that is not divisible by three. Twenty is also the number of faces on an icosahedron and vertices on a dodecahedron.
Nearby numbers
How to read this page
The factor list shows every way 20 splits into equal whole-number groups — 6 divisors in total. The prime factorisation is the compact form of that same information, and the base conversions restate 20 for contexts that do not use decimal.
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