The number 66991
66991 is a composite number with 4 divisors. Its prime factorisation is 31 × 2161. Divisors (4): 1, 31, 2161, 66991.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 66991: a Harshad number: divisible by its digit sum 31; a semiprime: 31 × 2161, the product of two primes.
- 2
66991 is composite. Its prime factorisation is
- 3
The divisors add up to 69184; without 66991 itself that is 2193, so 66991 is deficient (2193 is less than 66991). Euler's totient φ(66991) = 64800 numbers up to 66991 share no factor with it.
- 4
The digits of 66991 add up to 31, and repeating that until one digit is left gives the digital root 4. The Collatz sequence (halve if even, else 3n+1) takes 68 steps to reach 1.
LaTeX source of the formulas on this page
\[ 66991 = 31 \times 2161 \]
66991 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 69184 |
| Euler totient φ(n) | 64800 |
| Square | 4487794081 |
| Cube | 300641813280271 |
| Square root | 258.826197 |
| Digit sum / digital root | 31 / 4 |
| Collatz steps to 1 | 68 |
| Scientific notation | 6.6991 × |
66991 in other forms
| Form | Value |
|---|---|
| In words | sixty-six thousand nine hundred and ninety-one |
| Binary (base 2) | 10000010110101111 |
| Octal (base 8) | 202657 |
| Hexadecimal (base 16) | 105AF |
| Base 3 | 10101220011 |
| As time | 66991 seconds = 18 h 36 min 31 s |
Is 66991 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 1) | 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 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 7) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 4) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 1) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 1) | 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 66991 a prime number?
No. 66991 = 31 × 2161, so it is divisible by 31.
What are the factors of 66991?
1, 31, 2161, 66991.
What is 66991 in binary?
10000010110101111 (hexadecimal 105AF, octal 202657).
What is the square root of 66991?
About 258.8262.
Is 66991 divisible by 3?
No. Its digits add up to 31, which is not a multiple of 3.
What is special about the number 66991?
66991 is a Harshad number: divisible by its digit sum 31; a semiprime: 31 × 2161, the product of two primes.