The number 21311
21311 is a composite number with 4 divisors. Its prime factorisation is 101 × 211. Divisors (4): 1, 101, 211, 21311.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21311: a semiprime: 101 × 211, the product of two primes.
- 2
21311 is composite. Its prime factorisation is
- 3
The divisors add up to 21624; without 21311 itself that is 313, so 21311 is deficient (313 is less than 21311). Euler's totient φ(21311) = 21000 numbers up to 21311 share no factor with it.
- 4
The digits of 21311 add up to 8, and repeating that until one digit is left gives the digital root 8. The Collatz sequence (halve if even, else 3n+1) takes 149 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21311 = 101 \times 211 \]
21311 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 21624 |
| Euler totient φ(n) | 21000 |
| Square | 454158721 |
| Cube | 9678576503231 |
| Square root | 145.982876 |
| Digit sum / digital root | 8 / 8 |
| Collatz steps to 1 | 149 |
| Scientific notation | 2.1311 × |
21311 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand three hundred and eleven |
| Binary (base 2) | 101001100111111 |
| Octal (base 8) | 51477 |
| Hexadecimal (base 16) | 533F |
| Base 3 | 1002020022 |
| As time | 21311 seconds = 5 h 55 min 11 s |
Is 21311 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 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 7) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 8) | 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 4) | 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 21311 a prime number?
No. 21311 = 101 × 211, so it is divisible by 101.
What are the factors of 21311?
1, 101, 211, 21311.
What is 21311 in binary?
101001100111111 (hexadecimal 533F, octal 51477).
What is the square root of 21311?
About 145.9829.
Is 21311 divisible by 3?
No. Its digits add up to 8, which is not a multiple of 3.
What is special about the number 21311?
21311 is a semiprime: 101 × 211, the product of two primes.