The number 21988
21988 is a composite number with 12 divisors. Its prime factorisation is × 23 × 239. Divisors (12): 1, 2, 4, 23, 46, 92, 239, 478, 956, 5497, 10994, 21988.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
21988 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
21988 is composite. Its prime factorisation is
- 3
The divisors add up to 40320; without 21988 itself that is 18332, so 21988 is deficient (18332 is less than 21988). Euler's totient φ(21988) = 10472 numbers up to 21988 share no factor with it.
- 4
The digits of 21988 add up to 28, and repeating that until one digit is left gives the digital root 1. The Collatz sequence (halve if even, else 3n+1) takes 100 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21988 = 2^{2} \times 23 \times 239 \]21988 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 12 |
| Sum of divisors | 40320 |
| Euler totient φ(n) | 10472 |
| Square | 483472144 |
| Cube | 10630585502272 |
| Square root | 148.283512 (= 2√5497) |
| Digit sum / digital root | 28 / 1 |
| Collatz steps to 1 | 100 |
| Scientific notation | 2.1988 × |
21988 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand nine hundred and eighty-eight |
| Binary (base 2) | 101010111100100 |
| Octal (base 8) | 52744 |
| Hexadecimal (base 16) | 55E4 |
| Base 3 | 1010011101 |
| As time | 21988 seconds = 6 h 6 min 28 s |
Is 21988 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21988 ÷ 2 = 10994) | 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 | Yes (21988 ÷ 4 = 5497) | 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 4) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 1) | 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 4) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 1) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 8) | 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 4) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21988 a prime number?
No. 21988 = × 23 × 239, so it is divisible by 2.
What are the factors of 21988?
1, 2, 4, 23, 46, 92, 239, 478, 956, 5497, 10994, 21988.
What is 21988 in binary?
101010111100100 (hexadecimal 55E4, octal 52744).
What is the square root of 21988?
About 148.2835, exactly 2√5497.
Is 21988 divisible by 3?
No. Its digits add up to 28, which is not a multiple of 3.
What is special about the number 21988?
It is a composite number with 12 divisors.