The number 21240
21240 is a composite number with 48 divisors. Its prime factorisation is × × 5 × 59. Divisors (48): 1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 18, 20, 24, 30, 36 … 21240.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21240: a Harshad number: divisible by its digit sum 9.
- 2
21240 is composite. Its prime factorisation is
- 3
The divisors add up to 70200; without 21240 itself that is 48960, so 21240 is abundant (48960 is more than 21240). Euler's totient φ(21240) = 5568 numbers up to 21240 share no factor with it.
- 4
The digits of 21240 add up to 9, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 56 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21240 = 2^{3} \times 3^{2} \times 5 \times 59 \]21240 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 48 |
| Sum of divisors | 70200 |
| Euler totient φ(n) | 5568 |
| Square | 451137600 |
| Cube | 9582162624000 |
| Square root | 145.739494 (= 6√590) |
| Digit sum / digital root | 9 / 9 |
| Collatz steps to 1 | 56 |
| Scientific notation | 2.124 × |
21240 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand two hundred and forty |
| Binary (base 2) | 101001011111000 |
| Octal (base 8) | 51370 |
| Hexadecimal (base 16) | 52F8 |
| Base 3 | 1002010200 |
| As time | 21240 seconds = 5 h 54 min 0 s |
Is 21240 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (21240 ÷ 2 = 10620) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (21240 ÷ 3 = 7080) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | Yes (21240 ÷ 4 = 5310) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (21240 ÷ 5 = 4248) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | Yes (21240 ÷ 6 = 3540) | 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 | Yes (21240 ÷ 8 = 2655) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | Yes (21240 ÷ 9 = 2360) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | Yes (21240 ÷ 10 = 2124) | 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 | Yes (21240 ÷ 12 = 1770) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21240 a prime number?
No. 21240 = × × 5 × 59, so it is divisible by 2.
What are the factors of 21240?
1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 18, 20, 24, 30, 36, 40, 45, 59, 60, 72, 90, 118, 120, 177, 180, 236, 295, 354, 360, 472, 531, 590, 708, 885, 1062, 1180, 1416, 1770, 2124, 2360, 2655, 3540, 4248, 5310, 7080, 10620, 21240.
What is 21240 in binary?
101001011111000 (hexadecimal 52F8, octal 51370).
What is the square root of 21240?
About 145.7395, exactly 6√590.
Is 21240 divisible by 3?
Yes. Its digits add up to 9, a multiple of 3.
What is special about the number 21240?
21240 is a Harshad number: divisible by its digit sum 9.