The number 21011
21011 is a twin prime (21011 and 21013 are both prime) and the 2362nd prime number. Its only divisors are 1 and 21011.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21011: a twin prime (21011 and 21013 are both prime); the 2362nd prime number; a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
21011 is prime, so its only factors are 1 and 21011. It is the 2362nd prime; the next prime is 21013 and the one before is 21001.
- 3
The divisors add up to 21012; without 21011 itself that is 1, so 21011 is deficient (1 is less than 21011). Euler's totient φ(21011) = 21010 numbers up to 21011 share no factor with it.
- 4
The digits of 21011 add up to 5, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 149 steps to reach 1.
21011 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 21012 |
| Euler totient φ(n) | 21010 |
| Square | 441462121 |
| Cube | 9275560624331 |
| Square root | 144.951716 |
| Digit sum / digital root | 5 / 5 |
| Collatz steps to 1 | 149 |
| Scientific notation | 2.1011 × |
21011 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand and eleven |
| Binary (base 2) | 101001000010011 |
| Octal (base 8) | 51023 |
| Hexadecimal (base 16) | 5213 |
| Base 3 | 1001211012 |
| As time | 21011 seconds = 5 h 50 min 11 s |
Is 21011 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 2) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 3) | 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 5) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 4) | 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 3) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 5) | 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 11) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21011 a prime number?
Yes. 21011 is divisible only by 1 and itself.
What are the factors of 21011?
1, 21011.
What is 21011 in binary?
101001000010011 (hexadecimal 5213, octal 51023).
What is the square root of 21011?
About 144.9517.
Is 21011 divisible by 3?
No. Its digits add up to 5, which is not a multiple of 3.
What is special about the number 21011?
21011 is a twin prime (21011 and 21013 are both prime); the 2362nd prime number; a happy number: repeatedly adding the squares of its digits reaches 1.