The number 21997
21997 is the 2464th prime number. Its only divisors are 1 and 21997.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21997: the 2464th prime number.
- 2
21997 is prime, so its only factors are 1 and 21997. It is the 2464th prime; the next prime is 22003 and the one before is 21991.
- 3
The divisors add up to 21998; without 21997 itself that is 1, so 21997 is deficient (1 is less than 21997). Euler's totient φ(21997) = 21996 numbers up to 21997 share no factor with it.
- 4
The digits of 21997 add up to 28, and repeating that until one digit is left gives the digital root 1. The Collatz sequence (halve if even, else 3n+1) takes 69 steps to reach 1.
21997 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 21998 |
| Euler totient φ(n) | 21996 |
| Square | 483868009 |
| Cube | 10643644593973 |
| Square root | 148.313856 |
| Digit sum / digital root | 28 / 1 |
| Collatz steps to 1 | 69 |
| Scientific notation | 2.1997 × |
21997 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand nine hundred and ninety-seven |
| Binary (base 2) | 101010111101101 |
| Octal (base 8) | 52755 |
| Hexadecimal (base 16) | 55ED |
| Base 3 | 1010011201 |
| As time | 21997 seconds = 6 h 6 min 37 s |
Is 21997 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 1) | 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 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 5) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 1) | 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 8) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 1) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21997 a prime number?
Yes. 21997 is divisible only by 1 and itself.
What are the factors of 21997?
1, 21997.
What is 21997 in binary?
101010111101101 (hexadecimal 55ED, octal 52755).
What is the square root of 21997?
About 148.3139.
Is 21997 divisible by 3?
No. Its digits add up to 28, which is not a multiple of 3.
What is special about the number 21997?
21997 is the 2464th prime number.