The number 21281
21281 is a composite number with 4 divisors. Its prime factorisation is 13 × 1637. Divisors (4): 1, 13, 1637, 21281.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 21281: a semiprime: 13 × 1637, the product of two primes.
- 2
21281 is composite. Its prime factorisation is
- 3
The divisors add up to 22932; without 21281 itself that is 1651, so 21281 is deficient (1651 is less than 21281). Euler's totient φ(21281) = 19632 numbers up to 21281 share no factor with it.
- 4
The digits of 21281 add up to 14, and repeating that until one digit is left gives the digital root 5. The Collatz sequence (halve if even, else 3n+1) takes 100 steps to reach 1.
LaTeX source of the formulas on this page
\[ 21281 = 13 \times 1637 \]
21281 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 22932 |
| Euler totient φ(n) | 19632 |
| Square | 452880961 |
| Cube | 9637759731041 |
| Square root | 145.880088 |
| Digit sum / digital root | 14 / 5 |
| Collatz steps to 1 | 100 |
| Scientific notation | 2.1281 × |
21281 in other forms
| Form | Value |
|---|---|
| In words | twenty-one thousand two hundred and eighty-one |
| Binary (base 2) | 101001100100001 |
| Octal (base 8) | 51441 |
| Hexadecimal (base 16) | 5321 |
| Base 3 | 1002012012 |
| As time | 21281 seconds = 5 h 54 min 41 s |
Is 21281 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 1) | 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 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 7) | 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 21281 a prime number?
No. 21281 = 13 × 1637, so it is divisible by 13.
What are the factors of 21281?
1, 13, 1637, 21281.
What is 21281 in binary?
101001100100001 (hexadecimal 5321, octal 51441).
What is the square root of 21281?
About 145.8801.
Is 21281 divisible by 3?
No. Its digits add up to 14, which is not a multiple of 3.
What is special about the number 21281?
21281 is a semiprime: 13 × 1637, the product of two primes.