The number 21969
21969 is a composite number with 6 divisors. Its prime factorisation is × 2441. Divisors (6): 1, 3, 9, 2441, 7323, 21969.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21969: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
21969 is composite. Its prime factorisation is
- 3
The divisors add up to 31746; without 21969 itself that is 9777, so 21969 is deficient (9777 is less than 21969). Euler's totient φ(21969) = 14640 numbers up to 21969 share no factor with it.
- 4
The digits of 21969 add up to 27, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 43 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21969 = 3^{2} \times 2441 \]21969 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 6 |
| Sum of divisors | 31746 |
| Euler totient φ(n) | 14640 |
| Square | 482636961 |
| Cube | 10603051396209 |
| Square root | 148.219432 (= 3√2441) |
| Digit sum / digital root | 27 / 9 |
| Collatz steps to 1 | 43 |
| Scientific notation | 2.1969 × |
21969 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand nine hundred and sixty-nine |
| Binary (base 2) | 101010111010001 |
| Octal (base 8) | 52721 |
| Hexadecimal (base 16) | 55D1 |
| Base 3 | 1010010200 |
| As time | 21969 seconds = 6 h 6 min 9 s |
Is 21969 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 (21969 ÷ 3 = 7323) | 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 3) | 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 1) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | Yes (21969 ÷ 9 = 2441) | 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 2) | 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 21969 a prime number?
No. 21969 = × 2441, so it is divisible by 3.
What are the factors of 21969?
1, 3, 9, 2441, 7323, 21969.
What is 21969 in binary?
101010111010001 (hexadecimal 55D1, octal 52721).
What is the square root of 21969?
About 148.2194, exactly 3√2441.
Is 21969 divisible by 3?
Yes. Its digits add up to 27, a multiple of 3.
What is special about the number 21969?
21969 is a happy number: repeatedly adding the squares of its digits reaches 1.