The number 21823
21823 is a composite number with 4 divisors. Its prime factorisation is 139 × 157. Divisors (4): 1, 139, 157, 21823.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21823: a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 139 × 157, the product of two primes.
- 2
21823 is composite. Its prime factorisation is
- 3
The divisors add up to 22120; without 21823 itself that is 297, so 21823 is deficient (297 is less than 21823). Euler's totient φ(21823) = 21528 numbers up to 21823 share no factor with it.
- 4
The digits of 21823 add up to 16, and repeating that until one digit is left gives the digital root 7. The Collatz sequence (halve if even, else 3n+1) takes 193 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21823 = 139 \times 157 \]
21823 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 22120 |
| Euler totient φ(n) | 21528 |
| Square | 476243329 |
| Cube | 10393058168767 |
| Square root | 147.726098 |
| Digit sum / digital root | 16 / 7 |
| Collatz steps to 1 | 193 |
| Scientific notation | 2.1823 × |
21823 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand eight hundred and twenty-three |
| Binary (base 2) | 101010100111111 |
| Octal (base 8) | 52477 |
| Hexadecimal (base 16) | 553F |
| Base 3 | 1002221021 |
| As time | 21823 seconds = 6 h 3 min 43 s |
Is 21823 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 1) | 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 1) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 4) | 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 7) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 7) | 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 10) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 7) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21823 a prime number?
No. 21823 = 139 × 157, so it is divisible by 139.
What are the factors of 21823?
1, 139, 157, 21823.
What is 21823 in binary?
101010100111111 (hexadecimal 553F, octal 52477).
What is the square root of 21823?
About 147.7261.
Is 21823 divisible by 3?
No. Its digits add up to 16, which is not a multiple of 3.
What is special about the number 21823?
21823 is a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 139 × 157, the product of two primes.