The number 21918
21918 is a composite number with 16 divisors. Its prime factorisation is 2 × 3 × 13 × 281. Divisors (16): 1, 2, 3, 6, 13, 26, 39, 78, 281, 562, 843, 1686, 3653, 7306, 10959, 21918.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21918 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21918 is composite. Its prime factorisation is
- 3
The divisors add up to 47376; without 21918 itself that is 25458, so 21918 is abundant (25458 is more than 21918). Euler's totient φ(21918) = 6720 numbers up to 21918 share no factor with it.
- 4
The digits of 21918 add up to 21, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 193 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21918 = 2 \times 3 \times 13 \times 281 \]
21918 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 47376 |
| Euler totient φ(n) | 6720 |
| Square | 480398724 |
| Cube | 10529379232632 |
| Square root | 148.047290 |
| Digit sum / digital root | 21 / 3 |
| Collatz steps to 1 | 193 |
| Scientific notation | 2.1918 × |
21918 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand nine hundred and eighteen |
| Binary (base 2) | 101010110011110 |
| Octal (base 8) | 52636 |
| Hexadecimal (base 16) | 559E |
| Base 3 | 1010001210 |
| As time | 21918 seconds = 6 h 5 min 18 s |
Is 21918 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21918 ÷ 2 = 10959) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (21918 ÷ 3 = 7306) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 2) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | No (remainder 3) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | Yes (21918 ÷ 6 = 3653) | 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 6) | 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 | No (remainder 8) | 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 | No (remainder 6) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21918 a prime number?
No. 21918 = 2 × 3 × 13 × 281, so it is divisible by 2.
What are the factors of 21918?
1, 2, 3, 6, 13, 26, 39, 78, 281, 562, 843, 1686, 3653, 7306, 10959, 21918.
What is 21918 in binary?
101010110011110 (hexadecimal 559E, octal 52636).
What is the square root of 21918?
About 148.0473.
Is 21918 divisible by 3?
Yes. Its digits add up to 21, a multiple of 3.
What is special about the number 21918?
It is a composite number with 16 divisors.