The number 19987
19987 is a composite number with 8 divisors. Its prime factorisation is 11 × 23 × 79. Divisors (8): 1, 11, 23, 79, 253, 869, 1817, 19987.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
19987 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
19987 is composite. Its prime factorisation is
- 3
The divisors add up to 23040; without 19987 itself that is 3053, so 19987 is deficient (3053 is less than 19987). Euler's totient φ(19987) = 17160 numbers up to 19987 share no factor with it.
- 4
The digits of 19987 add up to 34, and repeating that until one digit is left gives the digital root 7. The Collatz sequence (halve if even, else 3n+1) takes 74 steps to reach 1.
LaTeX source of the formulas on this page
\[ 19987 = 11 \times 23 \times 79 \]
19987 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 23040 |
| Euler totient φ(n) | 17160 |
| Square | 399480169 |
| Cube | 7984410137803 |
| Square root | 141.375387 |
| Digit sum / digital root | 34 / 7 |
| Collatz steps to 1 | 74 |
| Scientific notation | 1.9987 × |
19987 in other forms
| Form | Value |
|---|---|
| In words | nineteen thousand nine hundred and eighty-seven |
| Binary (base 2) | 100111000010011 |
| Octal (base 8) | 47023 |
| Hexadecimal (base 16) | 4E13 |
| Base 3 | 1000102021 |
| As time | 19987 seconds = 5 h 33 min 7 s |
Is 19987 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 1) | 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 1) | 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 | No (remainder 3) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 7) | 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 | Yes (19987 ÷ 11 = 1817) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 7) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 19987 a prime number?
No. 19987 = 11 × 23 × 79, so it is divisible by 11.
What are the factors of 19987?
1, 11, 23, 79, 253, 869, 1817, 19987.
What is 19987 in binary?
100111000010011 (hexadecimal 4E13, octal 47023).
What is the square root of 19987?
About 141.3754.
Is 19987 divisible by 3?
No. Its digits add up to 34, which is not a multiple of 3.
What is special about the number 19987?
It is a composite number with 8 divisors.