The number 21816
21816 is a composite number with 32 divisors. Its prime factorisation is × × 101. Divisors (32): 1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 27, 36, 54, 72, 101, 108 … 21816.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21816: a Harshad number: divisible by its digit sum 18.
- 2
21816 is composite. Its prime factorisation is
- 3
The divisors add up to 61200; without 21816 itself that is 39384, so 21816 is abundant (39384 is more than 21816). Euler's totient φ(21816) = 7200 numbers up to 21816 share no factor with it.
- 4
The digits of 21816 add up to 18, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 131 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21816 = 2^{3} \times 3^{3} \times 101 \]21816 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 32 |
| Sum of divisors | 61200 |
| Euler totient φ(n) | 7200 |
| Square | 475937856 |
| Cube | 10383060266496 |
| Square root | 147.702404 (= 6√606) |
| Digit sum / digital root | 18 / 9 |
| Collatz steps to 1 | 131 |
| Scientific notation | 2.1816 × |
21816 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand eight hundred and sixteen |
| Binary (base 2) | 101010100111000 |
| Octal (base 8) | 52470 |
| Hexadecimal (base 16) | 5538 |
| Base 3 | 1002221000 |
| As time | 21816 seconds = 6 h 3 min 36 s |
Is 21816 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21816 ÷ 2 = 10908) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (21816 ÷ 3 = 7272) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | Yes (21816 ÷ 4 = 5454) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | No (remainder 1) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | Yes (21816 ÷ 6 = 3636) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 4) | 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 (21816 ÷ 8 = 2727) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | Yes (21816 ÷ 9 = 2424) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 6) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 3) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | Yes (21816 ÷ 12 = 1818) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21816 a prime number?
No. 21816 = × × 101, so it is divisible by 2.
What are the factors of 21816?
1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 27, 36, 54, 72, 101, 108, 202, 216, 303, 404, 606, 808, 909, 1212, 1818, 2424, 2727, 3636, 5454, 7272, 10908, 21816.
What is 21816 in binary?
101010100111000 (hexadecimal 5538, octal 52470).
What is the square root of 21816?
About 147.7024, exactly 6√606.
Is 21816 divisible by 3?
Yes. Its digits add up to 18, a multiple of 3.
What is special about the number 21816?
21816 is a Harshad number: divisible by its digit sum 18.