The number 77821
77821 is a composite number with 4 divisors. Its prime factorisation is 59 × 1319. Divisors (4): 1, 59, 1319, 77821.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 77821: a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 59 × 1319, the product of two primes.
- 2
77821 is composite. Its prime factorisation is
- 3
The divisors add up to 79200; without 77821 itself that is 1379, so 77821 is deficient (1379 is less than 77821). Euler's totient φ(77821) = 76444 numbers up to 77821 share no factor with it.
- 4
The digits of 77821 add up to 25, and repeating that until one digit is left gives the digital root 7. The Collatz sequence (halve if even, else 3n+1) takes 94 steps to reach 1.
LaTeX source of the formulas on this page
\[ 77821 = 59 \times 1319 \]
77821 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 79200 |
| Euler totient φ(n) | 76444 |
| Square | 6056108041 |
| Cube | 471292383858661 |
| Square root | 278.964155 |
| Digit sum / digital root | 25 / 7 |
| Collatz steps to 1 | 94 |
| Scientific notation | 7.7821 × |
77821 in other forms
| Form | Value |
|---|---|
| In words | seventy-seven thousand eight hundred and twenty-one |
| Binary (base 2) | 10010111111111101 |
| Octal (base 8) | 227775 |
| Hexadecimal (base 16) | 12FFD |
| Base 3 | 10221202021 |
| As time | 77821 seconds = 21 h 37 min 1 s |
Is 77821 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 1) | 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 1) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 2) | 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 7) | 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 1) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 77821 a prime number?
No. 77821 = 59 × 1319, so it is divisible by 59.
What are the factors of 77821?
1, 59, 1319, 77821.
What is 77821 in binary?
10010111111111101 (hexadecimal 12FFD, octal 227775).
What is the square root of 77821?
About 278.9642.
Is 77821 divisible by 3?
No. Its digits add up to 25, which is not a multiple of 3.
What is special about the number 77821?
77821 is a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 59 × 1319, the product of two primes.