The number 21999
21999 is a composite number with 4 divisors. Its prime factorisation is 3 × 7333. Divisors (4): 1, 3, 7333, 21999.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21999: a semiprime: 3 × 7333, the product of two primes.
- 2
21999 is composite. Its prime factorisation is
- 3
The divisors add up to 29336; without 21999 itself that is 7337, so 21999 is deficient (7337 is less than 21999). Euler's totient φ(21999) = 14664 numbers up to 21999 share no factor with it.
- 4
The digits of 21999 add up to 30, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 118 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21999 = 3 \times 7333 \]
21999 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 29336 |
| Euler totient φ(n) | 14664 |
| Square | 483956001 |
| Cube | 10646548065999 |
| Square root | 148.320599 |
| Digit sum / digital root | 30 / 3 |
| Collatz steps to 1 | 118 |
| Scientific notation | 2.1999 × |
21999 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand nine hundred and ninety-nine |
| Binary (base 2) | 101010111101111 |
| Octal (base 8) | 52757 |
| Hexadecimal (base 16) | 55EF |
| Base 3 | 1010011210 |
| As time | 21999 seconds = 6 h 6 min 39 s |
Is 21999 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 (21999 ÷ 3 = 7333) | 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 4) | 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 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 7) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 3) | 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 10) | 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 21999 a prime number?
No. 21999 = 3 × 7333, so it is divisible by 3.
What are the factors of 21999?
1, 3, 7333, 21999.
What is 21999 in binary?
101010111101111 (hexadecimal 55EF, octal 52757).
What is the square root of 21999?
About 148.3206.
Is 21999 divisible by 3?
Yes. Its digits add up to 30, a multiple of 3.
What is special about the number 21999?
21999 is a semiprime: 3 × 7333, the product of two primes.