The number 21971
21971 is a composite number with 4 divisors. Its prime factorisation is 127 × 173. Divisors (4): 1, 127, 173, 21971.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21971: a semiprime: 127 × 173, the product of two primes.
- 2
21971 is composite. Its prime factorisation is
- 3
The divisors add up to 22272; without 21971 itself that is 301, so 21971 is deficient (301 is less than 21971). Euler's totient φ(21971) = 21672 numbers up to 21971 share no factor with it.
- 4
The digits of 21971 add up to 20, and repeating that until one digit is left gives the digital root 2. The Collatz sequence (halve if even, else 3n+1) takes 162 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21971 = 127 \times 173 \]
21971 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 22272 |
| Euler totient φ(n) | 21672 |
| Square | 482724841 |
| Cube | 10605947481611 |
| Square root | 148.226179 |
| Digit sum / digital root | 20 / 2 |
| Collatz steps to 1 | 162 |
| Scientific notation | 2.1971 × |
21971 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand nine hundred and seventy-one |
| Binary (base 2) | 101010111010011 |
| Octal (base 8) | 52723 |
| Hexadecimal (base 16) | 55D3 |
| Base 3 | 1010010202 |
| As time | 21971 seconds = 6 h 6 min 11 s |
Is 21971 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 1) | 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 5) | 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 2) | 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 4) | 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 21971 a prime number?
No. 21971 = 127 × 173, so it is divisible by 127.
What are the factors of 21971?
1, 127, 173, 21971.
What is 21971 in binary?
101010111010011 (hexadecimal 55D3, octal 52723).
What is the square root of 21971?
About 148.2262.
Is 21971 divisible by 3?
No. Its digits add up to 20, which is not a multiple of 3.
What is special about the number 21971?
21971 is a semiprime: 127 × 173, the product of two primes.