The number 21841
21841 is a twin prime (21839 and 21841 are both prime) and the 2450th prime number. Its only divisors are 1 and 21841.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21841: a twin prime (21839 and 21841 are both prime); the 2450th prime number; a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
21841 is prime, so its only factors are 1 and 21841. It is the 2450th prime; the next prime is 21851 and the one before is 21839.
- 3
The divisors add up to 21842; without 21841 itself that is 1, so 21841 is deficient (1 is less than 21841). Euler's totient φ(21841) = 21840 numbers up to 21841 share no factor with it.
- 4
The digits of 21841 add up to 16, and repeating that until one digit is left gives the digital root 7. The Collatz sequence (halve if even, else 3n+1) takes 162 steps to reach 1.
21841 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 21842 |
| Euler totient φ(n) | 21840 |
| Square | 477029281 |
| Cube | 10418796526321 |
| Square root | 147.787009 |
| Digit sum / digital root | 16 / 7 |
| Collatz steps to 1 | 162 |
| Scientific notation | 2.1841 × |
21841 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand eight hundred and forty-one |
| Binary (base 2) | 101010101010001 |
| Octal (base 8) | 52521 |
| Hexadecimal (base 16) | 5551 |
| Base 3 | 1002221221 |
| As time | 21841 seconds = 6 h 4 min 1 s |
Is 21841 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 | No (remainder 1) | 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 1) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 1) | 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 1) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 7) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 1) | 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 1) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21841 a prime number?
Yes. 21841 is divisible only by 1 and itself.
What are the factors of 21841?
1, 21841.
What is 21841 in binary?
101010101010001 (hexadecimal 5551, octal 52521).
What is the square root of 21841?
About 147.7870.
Is 21841 divisible by 3?
No. Its digits add up to 16, which is not a multiple of 3.
What is special about the number 21841?
21841 is a twin prime (21839 and 21841 are both prime); the 2450th prime number; a happy number: repeatedly adding the squares of its digits reaches 1.