The number 21121
21121 is the 2374th prime number. Its only divisors are 1 and 21121.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21121: the 2374th prime number.
- 2
21121 is prime, so its only factors are 1 and 21121. It is the 2374th prime; the next prime is 21139 and the one before is 21107.
- 3
The divisors add up to 21122; without 21121 itself that is 1, so 21121 is deficient (1 is less than 21121). Euler's totient φ(21121) = 21120 numbers up to 21121 share no factor with it.
- 4
The digits of 21121 add up to 7, and repeating that until one digit is left gives the digital root 7. The Collatz sequence (halve if even, else 3n+1) takes 105 steps to reach 1.
21121 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 21122 |
| Euler totient φ(n) | 21120 |
| Square | 446096641 |
| Cube | 9422007154561 |
| Square root | 145.330657 |
| Digit sum / digital root | 7 / 7 |
| Collatz steps to 1 | 105 |
| Scientific notation | 2.1121 × |
21121 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand one hundred and twenty-one |
| Binary (base 2) | 101001010000001 |
| Octal (base 8) | 51201 |
| Hexadecimal (base 16) | 5281 |
| Base 3 | 1001222021 |
| As time | 21121 seconds = 5 h 52 min 1 s |
Is 21121 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 2) | 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 1) | 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 21121 a prime number?
Yes. 21121 is divisible only by 1 and itself.
What are the factors of 21121?
1, 21121.
What is 21121 in binary?
101001010000001 (hexadecimal 5281, octal 51201).
What is the square root of 21121?
About 145.3307.
Is 21121 divisible by 3?
No. Its digits add up to 7, which is not a multiple of 3.
What is special about the number 21121?
21121 is the 2374th prime number.