The number 21161
21161 is a composite number with 4 divisors. Its prime factorisation is 7 × 3023. Divisors (4): 1, 7, 3023, 21161.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21161: a semiprime: 7 × 3023, the product of two primes.
- 2
21161 is composite. Its prime factorisation is
- 3
The divisors add up to 24192; without 21161 itself that is 3031, so 21161 is deficient (3031 is less than 21161). Euler's totient φ(21161) = 18132 numbers up to 21161 share no factor with it.
- 4
The digits of 21161 add up to 11, and repeating that until one digit is left gives the digital root 2. The Collatz sequence (halve if even, else 3n+1) takes 131 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21161 = 7 \times 3023 \]
21161 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 24192 |
| Euler totient φ(n) | 18132 |
| Square | 447787921 |
| Cube | 9475640196281 |
| Square root | 145.468210 |
| Digit sum / digital root | 11 / 2 |
| Collatz steps to 1 | 131 |
| Scientific notation | 2.1161 × |
21161 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand one hundred and sixty-one |
| Binary (base 2) | 101001010101001 |
| Octal (base 8) | 51251 |
| Hexadecimal (base 16) | 52A9 |
| Base 3 | 1002000202 |
| As time | 21161 seconds = 5 h 52 min 41 s |
Is 21161 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 | Yes (21161 ÷ 7 = 3023) | 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 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 8) | 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 21161 a prime number?
No. 21161 = 7 × 3023, so it is divisible by 7.
What are the factors of 21161?
1, 7, 3023, 21161.
What is 21161 in binary?
101001010101001 (hexadecimal 52A9, octal 51251).
What is the square root of 21161?
About 145.4682.
Is 21161 divisible by 3?
No. Its digits add up to 11, which is not a multiple of 3.
What is special about the number 21161?
21161 is a semiprime: 7 × 3023, the product of two primes.