The number 77815
77815 is a triangular number: 1 + 2 + … + 394 = 77815. Its prime factorisation is 5 × 79 × 197. Divisors (8): 1, 5, 79, 197, 395, 985, 15563, 77815.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 77815: a triangular number: 1 + 2 + … + 394 = 77815; a happy number: repeatedly adding the squares of its digits reaches 1.
- 2
77815 is composite. Its prime factorisation is
- 3
The divisors add up to 95040; without 77815 itself that is 17225, so 77815 is deficient (17225 is less than 77815). Euler's totient φ(77815) = 61152 numbers up to 77815 share no factor with it.
- 4
The digits of 77815 add up to 28, and repeating that until one digit is left gives the digital root 1. The Collatz sequence (halve if even, else 3n+1) takes 130 steps to reach 1.
LaTeX source of the formulas on this page
\[ 77815 = 5 \times 79 \times 197 \]
77815 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 95040 |
| Euler totient φ(n) | 61152 |
| Square | 6055174225 |
| Cube | 471183382318375 |
| Square root | 278.953401 |
| Digit sum / digital root | 28 / 1 |
| Collatz steps to 1 | 130 |
| Scientific notation | 7.7815 × |
77815 in other forms
| Form | Value |
|---|---|
| In words | seventy-seven thousand eight hundred and fifteen |
| Binary (base 2) | 10010111111110111 |
| Octal (base 8) | 227767 |
| Hexadecimal (base 16) | 12FF7 |
| Base 3 | 10221202001 |
| As time | 77815 seconds = 21 h 36 min 55 s |
Is 77815 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 3) | A number is divisible by 4 if the last two digits make a multiple of 4. |
| 5 | Yes (77815 ÷ 5 = 15563) | 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 3) | 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 7) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 1) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 5) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 1) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 7) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 77815 a prime number?
No. 77815 = 5 × 79 × 197, so it is divisible by 5.
What are the factors of 77815?
1, 5, 79, 197, 395, 985, 15563, 77815.
What is 77815 in binary?
10010111111110111 (hexadecimal 12FF7, octal 227767).
What is the square root of 77815?
About 278.9534.
Is 77815 divisible by 3?
No. Its digits add up to 28, which is not a multiple of 3.
What is special about the number 77815?
77815 is a triangular number: 1 + 2 + … + 394 = 77815; a happy number: repeatedly adding the squares of its digits reaches 1.