The number 87
87 is a composite number with 4 divisors. Its prime factorisation is 3 × 29. Divisors (4): 1, 3, 29, 87.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 87: a semiprime: 3 × 29, the product of two primes.
- 2
87 is composite. Its prime factorisation is
- 3
The divisors add up to 120; without 87 itself that is 33, so 87 is deficient (33 is less than 87). Euler's totient φ(87) = 56 numbers up to 87 share no factor with it.
- 4
The digits of 87 add up to 15, and repeating that until one digit is left gives the digital root 6. The Collatz sequence (halve if even, else 3n+1) takes 30 steps to reach 1.
LaTeX source of the formulas on this page
\[ 87 = 3 \times 29 \]
87 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 120 |
| Euler totient φ(n) | 56 |
| Square | 7569 |
| Cube | 658503 |
| Square root | 9.327379 |
| Digit sum / digital root | 15 / 6 |
| Collatz steps to 1 | 30 |
| Scientific notation | 8.7 × |
87 in other forms
| Form | Value |
|---|---|
| In words | eighty-seven |
| Roman numerals | LXXXVII |
| Binary (base 2) | 1010111 |
| Octal (base 8) | 127 |
| Hexadecimal (base 16) | 57 |
| Base 3 | 10020 |
| As time | 87 seconds = 1 min 27 s |
Is 87 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 (87 ÷ 3 = 29) | 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 7) | 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 10) | 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 87 a prime number?
No. 87 = 3 × 29, so it is divisible by 3.
What are the factors of 87?
1, 3, 29, 87.
What is 87 in binary?
1010111 (hexadecimal 57, octal 127).
What is the square root of 87?
About 9.3274.
What is 87 in Roman numerals?
LXXXVII.
Is 87 divisible by 3?
Yes. Its digits add up to 15, a multiple of 3.
What is special about the number 87?
87 is a semiprime: 3 × 29, the product of two primes.