The number 21720
21720 is a composite number with 32 divisors. Its prime factorisation is × 3 × 5 × 181. Divisors (32): 1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 20, 24, 30, 40, 60, 120 … 21720.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21720: a Harshad number: divisible by its digit sum 12.
- 2
21720 is composite. Its prime factorisation is
- 3
The divisors add up to 65520; without 21720 itself that is 43800, so 21720 is abundant (43800 is more than 21720). Euler's totient φ(21720) = 5760 numbers up to 21720 share no factor with it.
- 4
The digits of 21720 add up to 12, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 100 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21720 = 2^{3} \times 3 \times 5 \times 181 \]21720 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 32 |
| Sum of divisors | 65520 |
| Euler totient φ(n) | 5760 |
| Square | 471758400 |
| Cube | 10246592448000 |
| Square root | 147.377067 (= 2√5430) |
| Digit sum / digital root | 12 / 3 |
| Collatz steps to 1 | 100 |
| Scientific notation | 2.172 × |
21720 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand seven hundred and twenty |
| Binary (base 2) | 101010011011000 |
| Octal (base 8) | 52330 |
| Hexadecimal (base 16) | 54D8 |
| Base 3 | 1002210110 |
| As time | 21720 seconds = 6 h 2 min 0 s |
Is 21720 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21720 ÷ 2 = 10860) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (21720 ÷ 3 = 7240) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | Yes (21720 ÷ 4 = 5430) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (21720 ÷ 5 = 4344) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | Yes (21720 ÷ 6 = 3620) | 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 | Yes (21720 ÷ 8 = 2715) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 3) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | Yes (21720 ÷ 10 = 2172) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 6) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | Yes (21720 ÷ 12 = 1810) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21720 a prime number?
No. 21720 = × 3 × 5 × 181, so it is divisible by 2.
What are the factors of 21720?
1, 2, 3, 4, 5, 6, 8, 10, 12, 15, 20, 24, 30, 40, 60, 120, 181, 362, 543, 724, 905, 1086, 1448, 1810, 2172, 2715, 3620, 4344, 5430, 7240, 10860, 21720.
What is 21720 in binary?
101010011011000 (hexadecimal 54D8, octal 52330).
What is the square root of 21720?
About 147.3771, exactly 2√5430.
Is 21720 divisible by 3?
Yes. Its digits add up to 12, a multiple of 3.
What is special about the number 21720?
21720 is a Harshad number: divisible by its digit sum 12.