The number 21978
21978 is a composite number with 32 divisors. Its prime factorisation is 2 × × 11 × 37. Divisors (32): 1, 2, 3, 6, 9, 11, 18, 22, 27, 33, 37, 54, 66, 74, 99, 111 … 21978.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21978: a Harshad number: divisible by its digit sum 27.
- 2
21978 is composite. Its prime factorisation is
- 3
The divisors add up to 54720; without 21978 itself that is 32742, so 21978 is abundant (32742 is more than 21978). Euler's totient φ(21978) = 6480 numbers up to 21978 share no factor with it.
- 4
The digits of 21978 add up to 27, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 69 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21978 = 2 \times 3^{3} \times 11 \times 37 \]21978 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 32 |
| Sum of divisors | 54720 |
| Euler totient φ(n) | 6480 |
| Square | 483032484 |
| Cube | 10616087933352 |
| Square root | 148.249789 (= 3√2442) |
| Digit sum / digital root | 27 / 9 |
| Collatz steps to 1 | 69 |
| Scientific notation | 2.1978 × |
21978 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand nine hundred and seventy-eight |
| Binary (base 2) | 101010111011010 |
| Octal (base 8) | 52732 |
| Hexadecimal (base 16) | 55DA |
| Base 3 | 1010011000 |
| As time | 21978 seconds = 6 h 6 min 18 s |
Is 21978 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21978 ÷ 2 = 10989) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (21978 ÷ 3 = 7326) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 2) | 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 | Yes (21978 ÷ 6 = 3663) | 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 2) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | Yes (21978 ÷ 9 = 2442) | 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 | Yes (21978 ÷ 11 = 1998) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 6) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21978 a prime number?
No. 21978 = 2 × × 11 × 37, so it is divisible by 2.
What are the factors of 21978?
1, 2, 3, 6, 9, 11, 18, 22, 27, 33, 37, 54, 66, 74, 99, 111, 198, 222, 297, 333, 407, 594, 666, 814, 999, 1221, 1998, 2442, 3663, 7326, 10989, 21978.
What is 21978 in binary?
101010111011010 (hexadecimal 55DA, octal 52732).
What is the square root of 21978?
About 148.2498, exactly 3√2442.
Is 21978 divisible by 3?
Yes. Its digits add up to 27, a multiple of 3.
What is special about the number 21978?
21978 is a Harshad number: divisible by its digit sum 27.