The number 81720
81720 is a composite number with 48 divisors. Its prime factorisation is × × 5 × 227. Divisors (48): 1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 18, 20, 24, 30, 36 … 81720.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 81720: a Harshad number: divisible by its digit sum 18.
- 2
81720 is composite. Its prime factorisation is
- 3
The divisors add up to 266760; without 81720 itself that is 185040, so 81720 is abundant (185040 is more than 81720). Euler's totient φ(81720) = 21696 numbers up to 81720 share no factor with it.
- 4
The digits of 81720 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 151 steps to reach 1.
LaTeX source of the formulas on this page
\[ 81720 = 2^{3} \times 3^{2} \times 5 \times 227 \]81720 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 48 |
| Sum of divisors | 266760 |
| Euler totient φ(n) | 21696 |
| Square | 6678158400 |
| Cube | 545739104448000 |
| Square root | 285.867102 (= 6√2270) |
| Digit sum / digital root | 18 / 9 |
| Collatz steps to 1 | 151 |
| Scientific notation | 8.172 × |
81720 in other forms
| Form | Value |
|---|---|
| In words | eighty-one thousand seven hundred and twenty |
| Binary (base 2) | 10011111100111000 |
| Octal (base 8) | 237470 |
| Hexadecimal (base 16) | 13F38 |
| Base 3 | 11011002200 |
| As time | 81720 seconds = 22 h 42 min 0 s |
Is 81720 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (81720 ÷ 2 = 40860) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (81720 ÷ 3 = 27240) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | Yes (81720 ÷ 4 = 20430) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (81720 ÷ 5 = 16344) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | Yes (81720 ÷ 6 = 13620) | 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 (81720 ÷ 8 = 10215) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | Yes (81720 ÷ 9 = 9080) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | Yes (81720 ÷ 10 = 8172) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 1) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | Yes (81720 ÷ 12 = 6810) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 81720 a prime number?
No. 81720 = × × 5 × 227, so it is divisible by 2.
What are the factors of 81720?
1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 18, 20, 24, 30, 36, 40, 45, 60, 72, 90, 120, 180, 227, 360, 454, 681, 908, 1135, 1362, 1816, 2043, 2270, 2724, 3405, 4086, 4540, 5448, 6810, 8172, 9080, 10215, 13620, 16344, 20430, 27240, 40860, 81720.
What is 81720 in binary?
10011111100111000 (hexadecimal 13F38, octal 237470).
What is the square root of 81720?
About 285.8671, exactly 6√2270.
Is 81720 divisible by 3?
Yes. Its digits add up to 18, a multiple of 3.
What is special about the number 81720?
81720 is a Harshad number: divisible by its digit sum 18.