The number 20987
20987 is a composite number with 4 divisors. Its prime factorisation is 31 × 677. Divisors (4): 1, 31, 677, 20987.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 20987: a semiprime: 31 × 677, the product of two primes.
- 2
20987 is composite. Its prime factorisation is
- 3
The divisors add up to 21696; without 20987 itself that is 709, so 20987 is deficient (709 is less than 20987). Euler's totient φ(20987) = 20280 numbers up to 20987 share no factor with it.
- 4
The digits of 20987 add up to 26, and repeating that until one digit is left gives the digital root 8. The Collatz sequence (halve if even, else 3n+1) takes 87 steps to reach 1.
LaTeX source of the formulas on this page
\[ 20987 = 31 \times 677 \]
20987 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 21696 |
| Euler totient φ(n) | 20280 |
| Square | 440454169 |
| Cube | 9243811644803 |
| Square root | 144.868906 |
| Digit sum / digital root | 26 / 8 |
| Collatz steps to 1 | 87 |
| Scientific notation | 2.0987 × |
20987 in other forms
| Form | Value |
|---|---|
| In words | twenty thousand nine hundred and eighty-seven |
| Binary (base 2) | 101000111111011 |
| Octal (base 8) | 50773 |
| Hexadecimal (base 16) | 51FB |
| Base 3 | 1001210022 |
| As time | 20987 seconds = 5 h 49 min 47 s |
Is 20987 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 | No (remainder 2) | 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 5) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 1) | 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 8) | 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 11) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 20987 a prime number?
No. 20987 = 31 × 677, so it is divisible by 31.
What are the factors of 20987?
1, 31, 677, 20987.
What is 20987 in binary?
101000111111011 (hexadecimal 51FB, octal 50773).
What is the square root of 20987?
About 144.8689.
Is 20987 divisible by 3?
No. Its digits add up to 26, which is not a multiple of 3.
What is special about the number 20987?
20987 is a semiprime: 31 × 677, the product of two primes.