The number 79821
79821 is a composite number with 18 divisors. Its prime factorisation is × × 181. Divisors (18): 1, 3, 7, 9, 21, 49, 63, 147, 181, 441, 543, 1267, 1629, 3801, 8869, 11403 … 79821.
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How to work it out
- 1
79821 has no famous special property in the usual lists (prime, square, cube, triangular, Fibonacci, palindrome, perfect), but it is still a composite number.
- 2
79821 is composite. Its prime factorisation is
- 3
The divisors add up to 134862; without 79821 itself that is 55041, so 79821 is deficient (55041 is less than 79821). Euler's totient φ(79821) = 45360 numbers up to 79821 share no factor with it.
- 4
The digits of 79821 add up to 27, and repeating that until one digit is left gives the digital root 9. The Collatz sequence (halve if even, else 3n+1) takes 45 steps to reach 1.
LaTeX source of the formulas on this page
\[ 79821 = 3^{2} \times 7^{2} \times 181 \]79821 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 18 |
| Sum of divisors | 134862 |
| Euler totient φ(n) | 45360 |
| Square | 6371392041 |
| Cube | 508570884104661 |
| Square root | 282.526105 (= 21√181) |
| Digit sum / digital root | 27 / 9 |
| Collatz steps to 1 | 45 |
| Scientific notation | 7.9821 × |
79821 in other forms
| Form | Value |
|---|---|
| In words | seventy-nine thousand eight hundred and twenty-one |
| Binary (base 2) | 10011011111001101 |
| Octal (base 8) | 233715 |
| Hexadecimal (base 16) | 137CD |
| Base 3 | 11001111100 |
| As time | 79821 seconds = 22 h 10 min 21 s |
Is 79821 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 (79821 ÷ 3 = 26607) | 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 | Yes (79821 ÷ 7 = 11403) | 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 | Yes (79821 ÷ 9 = 8869) | 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 9) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 79821 a prime number?
No. 79821 = × × 181, so it is divisible by 3.
What are the factors of 79821?
1, 3, 7, 9, 21, 49, 63, 147, 181, 441, 543, 1267, 1629, 3801, 8869, 11403, 26607, 79821.
What is 79821 in binary?
10011011111001101 (hexadecimal 137CD, octal 233715).
What is the square root of 79821?
About 282.5261, exactly 21√181.
Is 79821 divisible by 3?
Yes. Its digits add up to 27, a multiple of 3.
What is special about the number 79821?
It is a composite number with 18 divisors.