The number 21723
21723 is a composite number with 8 divisors. Its prime factorisation is 3 × 13 × 557. Divisors (8): 1, 3, 13, 39, 557, 1671, 7241, 21723.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21723 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21723 is composite. Its prime factorisation is
- 3
The divisors add up to 31248; without 21723 itself that is 9525, so 21723 is deficient (9525 is less than 21723). Euler's totient φ(21723) = 13344 numbers up to 21723 share no factor with it.
- 4
The digits of 21723 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 43 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21723 = 3 \times 13 \times 557 \]
21723 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 31248 |
| Euler totient φ(n) | 13344 |
| Square | 471888729 |
| Cube | 10250838860067 |
| Square root | 147.387245 |
| Digit sum / digital root | 15 / 6 |
| Collatz steps to 1 | 43 |
| Scientific notation | 2.1723 × |
21723 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand seven hundred and twenty-three |
| Binary (base 2) | 101010011011011 |
| Octal (base 8) | 52333 |
| Hexadecimal (base 16) | 54DB |
| Base 3 | 1002210120 |
| As time | 21723 seconds = 6 h 2 min 3 s |
Is 21723 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 (21723 ÷ 3 = 7241) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 3) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | No (remainder 3) | 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 2) | 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 3) | 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 3) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 9) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 3) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21723 a prime number?
No. 21723 = 3 × 13 × 557, so it is divisible by 3.
What are the factors of 21723?
1, 3, 13, 39, 557, 1671, 7241, 21723.
What is 21723 in binary?
101010011011011 (hexadecimal 54DB, octal 52333).
What is the square root of 21723?
About 147.3872.
Is 21723 divisible by 3?
Yes. Its digits add up to 15, a multiple of 3.
What is special about the number 21723?
It is a composite number with 8 divisors.