The number 21961
21961 is the 2461st prime number. Its only divisors are 1 and 21961.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21961: the 2461st prime number.
- 2
21961 is prime, so its only factors are 1 and 21961. It is the 2461st prime; the next prime is 21977 and the one before is 21943.
- 3
The divisors add up to 21962; without 21961 itself that is 1, so 21961 is deficient (1 is less than 21961). Euler's totient φ(21961) = 21960 numbers up to 21961 share no factor with it.
- 4
The digits of 21961 add up to 19, and repeating that until one digit is left gives the digital root 1. The Collatz sequence (halve if even, else 3n+1) takes 118 steps to reach 1.
21961 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 21962 |
| Euler totient φ(n) | 21960 |
| Square | 482285521 |
| Cube | 10591472326681 |
| Square root | 148.192442 |
| Digit sum / digital root | 19 / 1 |
| Collatz steps to 1 | 118 |
| Scientific notation | 2.1961 × |
21961 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand nine hundred and sixty-one |
| Binary (base 2) | 101010111001001 |
| Octal (base 8) | 52711 |
| Hexadecimal (base 16) | 55C9 |
| Base 3 | 1010010101 |
| As time | 21961 seconds = 6 h 6 min 1 s |
Is 21961 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 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 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 1) | 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 1) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 5) | 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 21961 a prime number?
Yes. 21961 is divisible only by 1 and itself.
What are the factors of 21961?
1, 21961.
What is 21961 in binary?
101010111001001 (hexadecimal 55C9, octal 52711).
What is the square root of 21961?
About 148.1924.
Is 21961 divisible by 3?
No. Its digits add up to 19, which is not a multiple of 3.
What is special about the number 21961?
21961 is the 2461st prime number.