The number 21749
21749 is a composite number with 8 divisors. Its prime factorisation is 7 × 13 × 239. Divisors (8): 1, 7, 13, 91, 239, 1673, 3107, 21749.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21749 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21749 is composite. Its prime factorisation is
- 3
The divisors add up to 26880; without 21749 itself that is 5131, so 21749 is deficient (5131 is less than 21749). Euler's totient φ(21749) = 17136 numbers up to 21749 share no factor with it.
- 4
The digits of 21749 add up to 23, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 69 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21749 = 7 \times 13 \times 239 \]
21749 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 26880 |
| Euler totient φ(n) | 17136 |
| Square | 473019001 |
| Cube | 10287690252749 |
| Square root | 147.475422 |
| Digit sum / digital root | 23 / 5 |
| Collatz steps to 1 | 69 |
| Scientific notation | 2.1749 × |
21749 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand seven hundred and forty-nine |
| Binary (base 2) | 101010011110101 |
| Octal (base 8) | 52365 |
| Hexadecimal (base 16) | 54F5 |
| Base 3 | 1002211112 |
| As time | 21749 seconds = 6 h 2 min 29 s |
Is 21749 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 | Yes (21749 ÷ 7 = 3107) | 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 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 2) | 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 21749 a prime number?
No. 21749 = 7 × 13 × 239, so it is divisible by 7.
What are the factors of 21749?
1, 7, 13, 91, 239, 1673, 3107, 21749.
What is 21749 in binary?
101010011110101 (hexadecimal 54F5, octal 52365).
What is the square root of 21749?
About 147.4754.
Is 21749 divisible by 3?
No. Its digits add up to 23, which is not a multiple of 3.
What is special about the number 21749?
It is a composite number with 8 divisors.