The number 21989
21989 is a composite number with 4 divisors. Its prime factorisation is 11 × 1999. Divisors (4): 1, 11, 1999, 21989.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21989: a semiprime: 11 × 1999, the product of two primes.
- 2
21989 is composite. Its prime factorisation is
- 3
The divisors add up to 24000; without 21989 itself that is 2011, so 21989 is deficient (2011 is less than 21989). Euler's totient φ(21989) = 19980 numbers up to 21989 share no factor with it.
- 4
The digits of 21989 add up to 29, and repeating that until one digit is left gives the digital root 2. The Collatz sequence (halve if even, else 3n+1) takes 100 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21989 = 11 \times 1999 \]
21989 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 24000 |
| Euler totient φ(n) | 19980 |
| Square | 483516121 |
| Cube | 10632035984669 |
| Square root | 148.286884 |
| Digit sum / digital root | 29 / 2 |
| Collatz steps to 1 | 100 |
| Scientific notation | 2.1989 × |
21989 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand nine hundred and eighty-nine |
| Binary (base 2) | 101010111100101 |
| Octal (base 8) | 52745 |
| Hexadecimal (base 16) | 55E5 |
| Base 3 | 1010011102 |
| As time | 21989 seconds = 6 h 6 min 29 s |
Is 21989 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 | 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 5) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 2) | 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 | Yes (21989 ÷ 11 = 1999) | 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 21989 a prime number?
No. 21989 = 11 × 1999, so it is divisible by 11.
What are the factors of 21989?
1, 11, 1999, 21989.
What is 21989 in binary?
101010111100101 (hexadecimal 55E5, octal 52745).
What is the square root of 21989?
About 148.2869.
Is 21989 divisible by 3?
No. Its digits add up to 29, which is not a multiple of 3.
What is special about the number 21989?
21989 is a semiprime: 11 × 1999, the product of two primes.