The number 21123
21123 is a composite number with 6 divisors. Its prime factorisation is × 2347. Divisors (6): 1, 3, 9, 2347, 7041, 21123.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21123: a happy number: repeatedly adding the squares of its digits reaches 1; a Harshad number: divisible by its digit sum 9.
- 2
21123 is composite. Its prime factorisation is
- 3
The divisors add up to 30524; without 21123 itself that is 9401, so 21123 is deficient (9401 is less than 21123). Euler's totient φ(21123) = 14076 numbers up to 21123 share no factor with it.
- 4
The digits of 21123 add up to 9, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 56 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21123 = 3^{2} \times 2347 \]21123 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 6 |
| Sum of divisors | 30524 |
| Euler totient φ(n) | 14076 |
| Square | 446181129 |
| Cube | 9424683987867 |
| Square root | 145.337538 (= 3√2347) |
| Digit sum / digital root | 9 / 9 |
| Collatz steps to 1 | 56 |
| Scientific notation | 2.1123 × |
21123 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand one hundred and twenty-three |
| Binary (base 2) | 101001010000011 |
| Octal (base 8) | 51203 |
| Hexadecimal (base 16) | 5283 |
| Base 3 | 1001222100 |
| As time | 21123 seconds = 5 h 52 min 3 s |
Is 21123 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 (21123 ÷ 3 = 7041) | 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 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 3) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | Yes (21123 ÷ 9 = 2347) | 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 3) | 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 21123 a prime number?
No. 21123 = × 2347, so it is divisible by 3.
What are the factors of 21123?
1, 3, 9, 2347, 7041, 21123.
What is 21123 in binary?
101001010000011 (hexadecimal 5283, octal 51203).
What is the square root of 21123?
About 145.3375, exactly 3√2347.
Is 21123 divisible by 3?
Yes. Its digits add up to 9, a multiple of 3.
What is special about the number 21123?
21123 is a happy number: repeatedly adding the squares of its digits reaches 1; a Harshad number: divisible by its digit sum 9.