The number 21421
21421 is a composite number with 4 divisors. Its prime factorisation is 31 × 691. Divisors (4): 1, 31, 691, 21421.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21421: a semiprime: 31 × 691, the product of two primes.
- 2
21421 is composite. Its prime factorisation is
- 3
The divisors add up to 22144; without 21421 itself that is 723, so 21421 is deficient (723 is less than 21421). Euler's totient φ(21421) = 20700 numbers up to 21421 share no factor with it.
- 4
The digits of 21421 add up to 10, and repeating that until one digit is left gives the digital root 1. The Collatz sequence (halve if even, else 3n+1) takes 100 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21421 = 31 \times 691 \]
21421 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 22144 |
| Euler totient φ(n) | 20700 |
| Square | 458859241 |
| Cube | 9829223801461 |
| Square root | 146.359147 |
| Digit sum / digital root | 10 / 1 |
| Collatz steps to 1 | 100 |
| Scientific notation | 2.1421 × |
21421 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand four hundred and twenty-one |
| Binary (base 2) | 101001110101101 |
| Octal (base 8) | 51655 |
| Hexadecimal (base 16) | 53AD |
| Base 3 | 1002101101 |
| As time | 21421 seconds = 5 h 57 min 1 s |
Is 21421 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 5) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 1) | 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 1) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21421 a prime number?
No. 21421 = 31 × 691, so it is divisible by 31.
What are the factors of 21421?
1, 31, 691, 21421.
What is 21421 in binary?
101001110101101 (hexadecimal 53AD, octal 51655).
What is the square root of 21421?
About 146.3591.
Is 21421 divisible by 3?
No. Its digits add up to 10, which is not a multiple of 3.
What is special about the number 21421?
21421 is a semiprime: 31 × 691, the product of two primes.