The number 20721
20721 is a composite number with 4 divisors. Its prime factorisation is 3 × 6907. Divisors (4): 1, 3, 6907, 20721.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 20721: a semiprime: 3 × 6907, the product of two primes.
- 2
20721 is composite. Its prime factorisation is
- 3
The divisors add up to 27632; without 20721 itself that is 6911, so 20721 is deficient (6911 is less than 20721). Euler's totient φ(20721) = 13812 numbers up to 20721 share no factor with it.
- 4
The digits of 20721 add up to 12, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 43 steps to reach 1.
LaTeX source of the formulas on this page
\[ 20721 = 3 \times 6907 \]
20721 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 27632 |
| Euler totient φ(n) | 13812 |
| Square | 429359841 |
| Cube | 8896765265361 |
| Square root | 143.947907 |
| Digit sum / digital root | 12 / 3 |
| Collatz steps to 1 | 43 |
| Scientific notation | 2.0721 × |
20721 in other forms
| Form | Value |
|---|---|
| In words | twenty thousand seven hundred and twenty-one |
| Binary (base 2) | 101000011110001 |
| Octal (base 8) | 50361 |
| Hexadecimal (base 16) | 50F1 |
| Base 3 | 1001102110 |
| As time | 20721 seconds = 5 h 45 min 21 s |
Is 20721 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 (20721 ÷ 3 = 6907) | 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 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 1) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 3) | 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 8) | 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 20721 a prime number?
No. 20721 = 3 × 6907, so it is divisible by 3.
What are the factors of 20721?
1, 3, 6907, 20721.
What is 20721 in binary?
101000011110001 (hexadecimal 50F1, octal 50361).
What is the square root of 20721?
About 143.9479.
Is 20721 divisible by 3?
Yes. Its digits add up to 12, a multiple of 3.
What is special about the number 20721?
20721 is a semiprime: 3 × 6907, the product of two primes.