The number 81987
81987 is a composite number with 4 divisors. Its prime factorisation is 3 × 27329. Divisors (4): 1, 3, 27329, 81987.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 81987: a semiprime: 3 × 27329, the product of two primes.
- 2
81987 is composite. Its prime factorisation is
- 3
The divisors add up to 109320; without 81987 itself that is 27333, so 81987 is deficient (27333 is less than 81987). Euler's totient φ(81987) = 54656 numbers up to 81987 share no factor with it.
- 4
The digits of 81987 add up to 33, and repeating that until one digit is left gives the digital root 6. The Collatz sequence (halve if even, else 3n+1) takes 63 steps to reach 1.
LaTeX source of the formulas on this page
\[ 81987 = 3 \times 27329 \]
81987 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 109320 |
| Euler totient φ(n) | 54656 |
| Square | 6721868169 |
| Cube | 551105805571803 |
| Square root | 286.333721 |
| Digit sum / digital root | 33 / 6 |
| Collatz steps to 1 | 63 |
| Scientific notation | 8.1987 × |
81987 in other forms
| Form | Value |
|---|---|
| In words | eighty-one thousand nine hundred and eighty-seven |
| Binary (base 2) | 10100000001000011 |
| Octal (base 8) | 240103 |
| Hexadecimal (base 16) | 14043 |
| Base 3 | 11011110120 |
| As time | 81987 seconds = 22 h 46 min 27 s |
Is 81987 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | No (remainder 1) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | Yes (81987 ÷ 3 = 27329) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | No (remainder 3) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | No (remainder 2) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 3) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 3) | 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 3) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 6) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 7) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 4) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 3) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 81987 a prime number?
No. 81987 = 3 × 27329, so it is divisible by 3.
What are the factors of 81987?
1, 3, 27329, 81987.
What is 81987 in binary?
10100000001000011 (hexadecimal 14043, octal 240103).
What is the square root of 81987?
About 286.3337.
Is 81987 divisible by 3?
Yes. Its digits add up to 33, a multiple of 3.
What is special about the number 81987?
81987 is a semiprime: 3 × 27329, the product of two primes.