The number 81440
81440 is a composite number with 24 divisors. Its prime factorisation is × 5 × 509. Divisors (24): 1, 2, 4, 5, 8, 10, 16, 20, 32, 40, 80, 160, 509, 1018, 2036, 2545 … 81440.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 81440: a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
81440 is composite. Its prime factorisation is
- 3
The divisors add up to 192780; without 81440 itself that is 111340, so 81440 is abundant (111340 is more than 81440). Euler's totient φ(81440) = 32512 numbers up to 81440 share no factor with it.
- 4
The digits of 81440 add up to 17, and repeating that until one digit is left gives the digital root 8. The Collatz sequence (halve if even, else 3n+1) takes 45 steps to reach 1.
LaTeX source of the formulas on this page
\[ 81440 = 2^{5} \times 5 \times 509 \]81440 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 24 |
| Sum of divisors | 192780 |
| Euler totient φ(n) | 32512 |
| Square | 6632473600 |
| Cube | 540148649984000 |
| Square root | 285.376944 (= 4√5090) |
| Digit sum / digital root | 17 / 8 |
| Collatz steps to 1 | 45 |
| Scientific notation | 8.144 × |
81440 in other forms
| Form | Value |
|---|---|
| In words | eighty-one thousand four hundred and forty |
| Binary (base 2) | 10011111000100000 |
| Octal (base 8) | 237040 |
| Hexadecimal (base 16) | 13E20 |
| Base 3 | 11010201022 |
| As time | 81440 seconds = 22 h 37 min 20 s |
Is 81440 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (81440 ÷ 2 = 40720) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | No (remainder 2) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | Yes (81440 ÷ 4 = 20360) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (81440 ÷ 5 = 16288) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 2) | 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 (81440 ÷ 8 = 10180) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 8) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | Yes (81440 ÷ 10 = 8144) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 7) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 8) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 81440 a prime number?
No. 81440 = × 5 × 509, so it is divisible by 2.
What are the factors of 81440?
1, 2, 4, 5, 8, 10, 16, 20, 32, 40, 80, 160, 509, 1018, 2036, 2545, 4072, 5090, 8144, 10180, 16288, 20360, 40720, 81440.
What is 81440 in binary?
10011111000100000 (hexadecimal 13E20, octal 237040).
What is the square root of 81440?
About 285.3769, exactly 4√5090.
Is 81440 divisible by 3?
No. Its digits add up to 17, which is not a multiple of 3.
What is special about the number 81440?
81440 is a happy number: repeatedly adding the squares of its digits reaches 1.