The number 21870
21870 is a composite number with 32 divisors. Its prime factorisation is 2 × × 5. Divisors (32): 1, 2, 3, 5, 6, 9, 10, 15, 18, 27, 30, 45, 54, 81, 90, 135 … 21870.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21870: a Harshad number: divisible by its digit sum 18.
- 2
21870 is composite. Its prime factorisation is
- 3
The divisors add up to 59040; without 21870 itself that is 37170, so 21870 is abundant (37170 is more than 21870). Euler's totient φ(21870) = 5832 numbers up to 21870 share no factor with it.
- 4
The digits of 21870 add up to 18, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 118 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21870 = 2 \times 3^{7} \times 5 \]21870 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 32 |
| Sum of divisors | 59040 |
| Euler totient φ(n) | 5832 |
| Square | 478296900 |
| Cube | 10460353203000 |
| Square root | 147.885091 (= 27√30) |
| Digit sum / digital root | 18 / 9 |
| Collatz steps to 1 | 118 |
| Scientific notation | 2.187 × |
21870 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand eight hundred and seventy |
| Binary (base 2) | 101010101101110 |
| Octal (base 8) | 52556 |
| Hexadecimal (base 16) | 556E |
| Base 3 | 1010000000 |
| As time | 21870 seconds = 6 h 4 min 30 s |
Is 21870 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21870 ÷ 2 = 10935) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (21870 ÷ 3 = 7290) | 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 | Yes (21870 ÷ 5 = 4374) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | Yes (21870 ÷ 6 = 3645) | 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 6) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | Yes (21870 ÷ 9 = 2430) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | Yes (21870 ÷ 10 = 2187) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 2) | 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 21870 a prime number?
No. 21870 = 2 × × 5, so it is divisible by 2.
What are the factors of 21870?
1, 2, 3, 5, 6, 9, 10, 15, 18, 27, 30, 45, 54, 81, 90, 135, 162, 243, 270, 405, 486, 729, 810, 1215, 1458, 2187, 2430, 3645, 4374, 7290, 10935, 21870.
What is 21870 in binary?
101010101101110 (hexadecimal 556E, octal 52556).
What is the square root of 21870?
About 147.8851, exactly 27√30.
Is 21870 divisible by 3?
Yes. Its digits add up to 18, a multiple of 3.
What is special about the number 21870?
21870 is a Harshad number: divisible by its digit sum 18.