The number 21101
21101 is the 2372nd prime number. Its only divisors are 1 and 21101.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21101: the 2372nd prime number; a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
21101 is prime, so its only factors are 1 and 21101. It is the 2372nd prime; the next prime is 21107 and the one before is 21089.
- 3
The divisors add up to 21102; without 21101 itself that is 1, so 21101 is deficient (1 is less than 21101). Euler's totient φ(21101) = 21100 numbers up to 21101 share no factor with it.
- 4
The digits of 21101 add up to 5, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 105 steps to reach 1.
21101 at a glance
| Property | Value |
|---|---|
| Type | prime |
| Number of divisors | 2 |
| Sum of divisors | 21102 |
| Euler totient φ(n) | 21100 |
| Square | 445252201 |
| Cube | 9395266693301 |
| Square root | 145.261833 |
| Digit sum / digital root | 5 / 5 |
| Collatz steps to 1 | 105 |
| Scientific notation | 2.1101 × |
21101 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand one hundred and one |
| Binary (base 2) | 101001001101101 |
| Octal (base 8) | 51155 |
| Hexadecimal (base 16) | 526D |
| Base 3 | 1001221112 |
| As time | 21101 seconds = 5 h 51 min 41 s |
Is 21101 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 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 5) | 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 5) | 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 3) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 5) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 21101 a prime number?
Yes. 21101 is divisible only by 1 and itself.
What are the factors of 21101?
1, 21101.
What is 21101 in binary?
101001001101101 (hexadecimal 526D, octal 51155).
What is the square root of 21101?
About 145.2618.
Is 21101 divisible by 3?
No. Its digits add up to 5, which is not a multiple of 3.
What is special about the number 21101?
21101 is the 2372nd prime number; a happy number: repeatedly adding the squares of its digits reaches 1.