The number 21409
21409 is a composite number with 4 divisors. Its prime factorisation is 79 × 271. Divisors (4): 1, 79, 271, 21409.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21409: a semiprime: 79 × 271, the product of two primes.
- 2
21409 is composite. Its prime factorisation is
- 3
The divisors add up to 21760; without 21409 itself that is 351, so 21409 is deficient (351 is less than 21409). Euler's totient φ(21409) = 21060 numbers up to 21409 share no factor with it.
- 4
The digits of 21409 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 56 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21409 = 79 \times 271 \]
21409 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 21760 |
| Euler totient φ(n) | 21060 |
| Square | 458345281 |
| Cube | 9812714120929 |
| Square root | 146.318147 |
| Digit sum / digital root | 16 / 7 |
| Collatz steps to 1 | 56 |
| Scientific notation | 2.1409 × |
21409 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand four hundred and nine |
| Binary (base 2) | 101001110100001 |
| Octal (base 8) | 51641 |
| Hexadecimal (base 16) | 53A1 |
| Base 3 | 1002100221 |
| As time | 21409 seconds = 5 h 56 min 49 s |
Is 21409 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 4) | 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 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 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 9) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 3) | 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 21409 a prime number?
No. 21409 = 79 × 271, so it is divisible by 79.
What are the factors of 21409?
1, 79, 271, 21409.
What is 21409 in binary?
101001110100001 (hexadecimal 53A1, octal 51641).
What is the square root of 21409?
About 146.3181.
Is 21409 divisible by 3?
No. Its digits add up to 16, which is not a multiple of 3.
What is special about the number 21409?
21409 is a semiprime: 79 × 271, the product of two primes.