The number 21820
21820 is a composite number with 12 divisors. Its prime factorisation is × 5 × 1091. Divisors (12): 1, 2, 4, 5, 10, 20, 1091, 2182, 4364, 5455, 10910, 21820.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21820 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21820 is composite. Its prime factorisation is
- 3
The divisors add up to 45864; without 21820 itself that is 24044, so 21820 is abundant (24044 is more than 21820). Euler's totient φ(21820) = 8720 numbers up to 21820 share no factor with it.
- 4
The digits of 21820 add up to 13, and repeating that until one digit is left gives the digital root 4. The Collatz sequence (halve if even, else 3n+1) takes 131 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21820 = 2^{2} \times 5 \times 1091 \]21820 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 12 |
| Sum of divisors | 45864 |
| Euler totient φ(n) | 8720 |
| Square | 476112400 |
| Cube | 10388772568000 |
| Square root | 147.715944 (= 2√5455) |
| Digit sum / digital root | 13 / 4 |
| Collatz steps to 1 | 131 |
| Scientific notation | 2.182 × |
21820 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand eight hundred and twenty |
| Binary (base 2) | 101010100111100 |
| Octal (base 8) | 52474 |
| Hexadecimal (base 16) | 553C |
| Base 3 | 1002221011 |
| As time | 21820 seconds = 6 h 3 min 40 s |
Is 21820 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21820 ÷ 2 = 10910) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | No (remainder 1) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | Yes (21820 ÷ 4 = 5455) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (21820 ÷ 5 = 4364) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 4) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 1) | 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 4) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | Yes (21820 ÷ 10 = 2182) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 7) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 4) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21820 a prime number?
No. 21820 = × 5 × 1091, so it is divisible by 2.
What are the factors of 21820?
1, 2, 4, 5, 10, 20, 1091, 2182, 4364, 5455, 10910, 21820.
What is 21820 in binary?
101010100111100 (hexadecimal 553C, octal 52474).
What is the square root of 21820?
About 147.7159, exactly 2√5455.
Is 21820 divisible by 3?
No. Its digits add up to 13, which is not a multiple of 3.
What is special about the number 21820?
It is a composite number with 12 divisors.