The number 16721
16721 is a composite number with 4 divisors. Its prime factorisation is 23 × 727. Divisors (4): 1, 23, 727, 16721.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 16721: a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 23 × 727, the product of two primes.
- 2
16721 is composite. Its prime factorisation is
- 3
The divisors add up to 17472; without 16721 itself that is 751, so 16721 is deficient (751 is less than 16721). Euler's totient φ(16721) = 15972 numbers up to 16721 share no factor with it.
- 4
The digits of 16721 add up to 17, and repeating that until one digit is left gives the digital root 8. The Collatz sequence (halve if even, else 3n+1) takes 66 steps to reach 1.
LaTeX source of the formulas on this page
\[ 16721 = 23 \times 727 \]
16721 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 17472 |
| Euler totient φ(n) | 15972 |
| Square | 279591841 |
| Cube | 4675055173361 |
| Square root | 129.309706 |
| Digit sum / digital root | 17 / 8 |
| Collatz steps to 1 | 66 |
| Scientific notation | 1.6721 × |
16721 in other forms
| Form | Value |
|---|---|
| In words | sixteen thousand seven hundred and twenty-one |
| Binary (base 2) | 100000101010001 |
| Octal (base 8) | 40521 |
| Hexadecimal (base 16) | 4151 |
| Base 3 | 211221022 |
| As time | 16721 seconds = 4 h 38 min 41 s |
Is 16721 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 1) | 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 5) | 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 8) | 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 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 16721 a prime number?
No. 16721 = 23 × 727, so it is divisible by 23.
What are the factors of 16721?
1, 23, 727, 16721.
What is 16721 in binary?
100000101010001 (hexadecimal 4151, octal 40521).
What is the square root of 16721?
About 129.3097.
Is 16721 divisible by 3?
No. Its digits add up to 17, which is not a multiple of 3.
What is special about the number 16721?
16721 is a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 23 × 727, the product of two primes.