The number 81380
81380 is a composite number with 24 divisors. Its prime factorisation is × 5 × 13 × 313. Divisors (24): 1, 2, 4, 5, 10, 13, 20, 26, 52, 65, 130, 260, 313, 626, 1252, 1565 … 81380.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 81380: a Harshad number: divisible by its digit sum 20.
- 2
81380 is composite. Its prime factorisation is
- 3
The divisors add up to 184632; without 81380 itself that is 103252, so 81380 is abundant (103252 is more than 81380). Euler's totient φ(81380) = 29952 numbers up to 81380 share no factor with it.
- 4
The digits of 81380 add up to 20, and repeating that until one digit is left gives the digital root 2. The Collatz sequence (halve if even, else 3n+1) takes 89 steps to reach 1.
LaTeX source of the formulas on this page
\[ 81380 = 2^{2} \times 5 \times 13 \times 313 \]81380 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 24 |
| Sum of divisors | 184632 |
| Euler totient φ(n) | 29952 |
| Square | 6622704400 |
| Cube | 538955684072000 |
| Square root | 285.271800 (= 2√20345) |
| Digit sum / digital root | 20 / 2 |
| Collatz steps to 1 | 89 |
| Scientific notation | 8.138 × |
81380 in other forms
| Form | Value |
|---|---|
| In words | eighty-one thousand three hundred and eighty |
| Binary (base 2) | 10011110111100100 |
| Octal (base 8) | 236744 |
| Hexadecimal (base 16) | 13DE4 |
| Base 3 | 11010122002 |
| As time | 81380 seconds = 22 h 36 min 20 s |
Is 81380 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (81380 ÷ 2 = 40690) | 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 (81380 ÷ 4 = 20345) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (81380 ÷ 5 = 16276) | 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 5) | 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 4) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 2) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | Yes (81380 ÷ 10 = 8138) | 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 8) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 81380 a prime number?
No. 81380 = × 5 × 13 × 313, so it is divisible by 2.
What are the factors of 81380?
1, 2, 4, 5, 10, 13, 20, 26, 52, 65, 130, 260, 313, 626, 1252, 1565, 3130, 4069, 6260, 8138, 16276, 20345, 40690, 81380.
What is 81380 in binary?
10011110111100100 (hexadecimal 13DE4, octal 236744).
What is the square root of 81380?
About 285.2718, exactly 2√20345.
Is 81380 divisible by 3?
No. Its digits add up to 20, which is not a multiple of 3.
What is special about the number 81380?
81380 is a Harshad number: divisible by its digit sum 20.