The number 21309
21309 is a composite number with 4 divisors. Its prime factorisation is 3 × 7103. Divisors (4): 1, 3, 7103, 21309.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21309: a semiprime: 3 × 7103, the product of two primes.
- 2
21309 is composite. Its prime factorisation is
- 3
The divisors add up to 28416; without 21309 itself that is 7107, so 21309 is deficient (7107 is less than 21309). Euler's totient φ(21309) = 14204 numbers up to 21309 share no factor with it.
- 4
The digits of 21309 add up to 15, and repeating that until one digit is left gives the digital root 6. The Collatz sequence (halve if even, else 3n+1) takes 87 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21309 = 3 \times 7103 \]
21309 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 28416 |
| Euler totient φ(n) | 14204 |
| Square | 454073481 |
| Cube | 9675851806629 |
| Square root | 145.976025 |
| Digit sum / digital root | 15 / 6 |
| Collatz steps to 1 | 87 |
| Scientific notation | 2.1309 × |
21309 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand three hundred and nine |
| Binary (base 2) | 101001100111101 |
| Octal (base 8) | 51475 |
| Hexadecimal (base 16) | 533D |
| Base 3 | 1002020020 |
| As time | 21309 seconds = 5 h 55 min 9 s |
Is 21309 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 | Yes (21309 ÷ 3 = 7103) | 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 3) | 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 6) | 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 2) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21309 a prime number?
No. 21309 = 3 × 7103, so it is divisible by 3.
What are the factors of 21309?
1, 3, 7103, 21309.
What is 21309 in binary?
101001100111101 (hexadecimal 533D, octal 51475).
What is the square root of 21309?
About 145.9760.
Is 21309 divisible by 3?
Yes. Its digits add up to 15, a multiple of 3.
What is special about the number 21309?
21309 is a semiprime: 3 × 7103, the product of two primes.