The number 21909
21909 is a composite number with 8 divisors. Its prime factorisation is 3 × 67 × 109. Divisors (8): 1, 3, 67, 109, 201, 327, 7303, 21909.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21909: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
21909 is composite. Its prime factorisation is
- 3
The divisors add up to 29920; without 21909 itself that is 8011, so 21909 is deficient (8011 is less than 21909). Euler's totient φ(21909) = 14256 numbers up to 21909 share no factor with it.
- 4
The digits of 21909 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 43 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21909 = 3 \times 67 \times 109 \]
21909 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 29920 |
| Euler totient φ(n) | 14256 |
| Square | 480004281 |
| Cube | 10516413792429 |
| Square root | 148.016891 |
| Digit sum / digital root | 21 / 3 |
| Collatz steps to 1 | 43 |
| Scientific notation | 2.1909 × |
21909 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand nine hundred and nine |
| Binary (base 2) | 101010110010101 |
| Octal (base 8) | 52625 |
| Hexadecimal (base 16) | 5595 |
| Base 3 | 1010001110 |
| As time | 21909 seconds = 6 h 5 min 9 s |
Is 21909 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | No (remainder 1) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (21909 ÷ 3 = 7303) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 1) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | No (remainder 4) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 3) | 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 5) | 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 9) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 8) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21909 a prime number?
No. 21909 = 3 × 67 × 109, so it is divisible by 3.
What are the factors of 21909?
1, 3, 67, 109, 201, 327, 7303, 21909.
What is 21909 in binary?
101010110010101 (hexadecimal 5595, octal 52625).
What is the square root of 21909?
About 148.0169.
Is 21909 divisible by 3?
Yes. Its digits add up to 21, a multiple of 3.
What is special about the number 21909?
21909 is a happy number: repeatedly adding the squares of its digits reaches 1.