The number 19821
19821 is a composite number with 4 divisors. Its prime factorisation is 3 × 6607. Divisors (4): 1, 3, 6607, 19821.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 19821: a semiprime: 3 × 6607, the product of two primes.
- 2
19821 is composite. Its prime factorisation is
- 3
The divisors add up to 26432; without 19821 itself that is 6611, so 19821 is deficient (6611 is less than 19821). Euler's totient φ(19821) = 13212 numbers up to 19821 share no factor with it.
- 4
The digits of 19821 add up to 21, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 74 steps to reach 1.
LaTeX source of the formulas on this page
\[ 19821 = 3 \times 6607 \]
19821 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 26432 |
| Euler totient φ(n) | 13212 |
| Square | 392872041 |
| Cube | 7787116724661 |
| Square root | 140.787073 |
| Digit sum / digital root | 21 / 3 |
| Collatz steps to 1 | 74 |
| Scientific notation | 1.9821 × |
19821 in other forms
| Form | Value |
|---|---|
| In words | nineteen thousand eight hundred and twenty-one |
| Binary (base 2) | 100110101101101 |
| Octal (base 8) | 46555 |
| Hexadecimal (base 16) | 4D6D |
| Base 3 | 1000012010 |
| As time | 19821 seconds = 5 h 30 min 21 s |
Is 19821 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 | Yes (19821 ÷ 3 = 6607) | 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 3) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 4) | 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 3) | 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 10) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 19821 a prime number?
No. 19821 = 3 × 6607, so it is divisible by 3.
What are the factors of 19821?
1, 3, 6607, 19821.
What is 19821 in binary?
100110101101101 (hexadecimal 4D6D, octal 46555).
What is the square root of 19821?
About 140.7871.
Is 19821 divisible by 3?
Yes. Its digits add up to 21, a multiple of 3.
What is special about the number 19821?
19821 is a semiprime: 3 × 6607, the product of two primes.