The number 20
20 is a composite number with 6 divisors. Its prime factorisation is × 5. Divisors (6): 1, 2, 4, 5, 10, 20.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 20: a Harshad number: divisible by its digit sum 2.
- 2
20 is composite. Its prime factorisation is
- 3
The divisors add up to 42; without 20 itself that is 22, so 20 is abundant (22 is more than 20). Euler's totient φ(20) = 8 numbers up to 20 share no factor with it.
- 4
The digits of 20 add up to 2, and repeating that until one digit is left gives the digital root 2. The Collatz sequence (halve if even, else 3n+1) takes 7 steps to reach 1.
LaTeX source of the formulas on this page
\[ 20 = 2^{2} \times 5 \]20 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 6 |
| Sum of divisors | 42 |
| Euler totient φ(n) | 8 |
| Square | 400 |
| Cube | 8000 |
| Square root | 4.472136 (= 2√5) |
| Digit sum / digital root | 2 / 2 |
| Collatz steps to 1 | 7 |
| Scientific notation | 2 × |
20 in other forms
| Form | Value |
|---|---|
| In words | twenty |
| Roman numerals | XX |
| Binary (base 2) | 10100 |
| Octal (base 8) | 24 |
| Hexadecimal (base 16) | 14 |
| Base 3 | 202 |
| As time | 20 seconds |
Is 20 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (20 ÷ 2 = 10) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | No (remainder 2) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | Yes (20 ÷ 4 = 5) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (20 ÷ 5 = 4) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 2) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 6) | A number is divisible by 7 if double the last digit and subtract it from the rest: the result is a multiple of 7. |
| 8 | No (remainder 4) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 2) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | Yes (20 ÷ 10 = 2) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 9) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 8) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 20 a prime number?
No. 20 = × 5, so it is divisible by 2.
What are the factors of 20?
1, 2, 4, 5, 10, 20.
What is 20 in binary?
10100 (hexadecimal 14, octal 24).
What is the square root of 20?
About 4.4721, exactly 2√5.
What is 20 in Roman numerals?
XX.
Is 20 divisible by 3?
No. Its digits add up to 2, which is not a multiple of 3.
What is special about the number 20?
20 is a Harshad number: divisible by its digit sum 2.