The number 21209
21209 is a composite number with 4 divisors. Its prime factorisation is 127 × 167. Divisors (4): 1, 127, 167, 21209.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21209: a semiprime: 127 × 167, the product of two primes.
- 2
21209 is composite. Its prime factorisation is
- 3
The divisors add up to 21504; without 21209 itself that is 295, so 21209 is deficient (295 is less than 21209). Euler's totient φ(21209) = 20916 numbers up to 21209 share no factor with it.
- 4
The digits of 21209 add up to 14, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 100 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21209 = 127 \times 167 \]
21209 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 21504 |
| Euler totient φ(n) | 20916 |
| Square | 449821681 |
| Cube | 9540268032329 |
| Square root | 145.633101 |
| Digit sum / digital root | 14 / 5 |
| Collatz steps to 1 | 100 |
| Scientific notation | 2.1209 × |
21209 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand two hundred and nine |
| Binary (base 2) | 101001011011001 |
| Octal (base 8) | 51331 |
| Hexadecimal (base 16) | 52D9 |
| Base 3 | 1002002112 |
| As time | 21209 seconds = 5 h 53 min 29 s |
Is 21209 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 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 5) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 6) | 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 5) | 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 1) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 5) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21209 a prime number?
No. 21209 = 127 × 167, so it is divisible by 127.
What are the factors of 21209?
1, 127, 167, 21209.
What is 21209 in binary?
101001011011001 (hexadecimal 52D9, octal 51331).
What is the square root of 21209?
About 145.6331.
Is 21209 divisible by 3?
No. Its digits add up to 14, which is not a multiple of 3.
What is special about the number 21209?
21209 is a semiprime: 127 × 167, the product of two primes.