The number 21378
21378 is a composite number with 16 divisors. Its prime factorisation is 2 × 3 × 7 × 509. Divisors (16): 1, 2, 3, 6, 7, 14, 21, 42, 509, 1018, 1527, 3054, 3563, 7126, 10689, 21378.
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How to work it out
- 1
What is special about 21378: a Harshad number: divisible by its digit sum 21.
- 2
21378 is composite. Its prime factorisation is
- 3
The divisors add up to 48960; without 21378 itself that is 27582, so 21378 is abundant (27582 is more than 21378). Euler's totient φ(21378) = 6096 numbers up to 21378 share no factor with it.
- 4
The digits of 21378 add up to 21, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 149 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21378 = 2 \times 3 \times 7 \times 509 \]
21378 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 16 |
| Sum of divisors | 48960 |
| Euler totient φ(n) | 6096 |
| Square | 457018884 |
| Cube | 9770149702152 |
| Square root | 146.212175 |
| Digit sum / digital root | 21 / 3 |
| Collatz steps to 1 | 149 |
| Scientific notation | 2.1378 × |
21378 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand three hundred and seventy-eight |
| Binary (base 2) | 101001110000010 |
| Octal (base 8) | 51602 |
| Hexadecimal (base 16) | 5382 |
| Base 3 | 1002022210 |
| As time | 21378 seconds = 5 h 56 min 18 s |
Is 21378 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21378 ÷ 2 = 10689) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (21378 ÷ 3 = 7126) | 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 (21378 ÷ 6 = 3563) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | Yes (21378 ÷ 7 = 3054) | 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 | No (remainder 3) | 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 5) | 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 21378 a prime number?
No. 21378 = 2 × 3 × 7 × 509, so it is divisible by 2.
What are the factors of 21378?
1, 2, 3, 6, 7, 14, 21, 42, 509, 1018, 1527, 3054, 3563, 7126, 10689, 21378.
What is 21378 in binary?
101001110000010 (hexadecimal 5382, octal 51602).
What is the square root of 21378?
About 146.2122.
Is 21378 divisible by 3?
Yes. Its digits add up to 21, a multiple of 3.
What is special about the number 21378?
21378 is a Harshad number: divisible by its digit sum 21.