The number 123
123 is a composite number with 4 divisors. Its prime factorisation is 3 × 41. Divisors (4): 1, 3, 41, 123.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 123: a semiprime: 3 × 41, the product of two primes.
- 2
123 is composite. Its prime factorisation is
- 3
The divisors add up to 168; without 123 itself that is 45, so 123 is deficient (45 is less than 123). Euler's totient φ(123) = 80 numbers up to 123 share no factor with it.
- 4
The digits of 123 add up to 6, and repeating that until one digit is left gives the digital root 6. The Collatz sequence (halve if even, else 3n+1) takes 46 steps to reach 1.
LaTeX source of the formulas on this page
\[ 123 = 3 \times 41 \]
123 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 168 |
| Euler totient φ(n) | 80 |
| Square | 15129 |
| Cube | 1860867 |
| Square root | 11.090537 |
| Digit sum / digital root | 6 / 6 |
| Collatz steps to 1 | 46 |
| Scientific notation | 1.23 × |
123 in other forms
| Form | Value |
|---|---|
| In words | one hundred and twenty-three |
| Roman numerals | CXXIII |
| Binary (base 2) | 1111011 |
| Octal (base 8) | 173 |
| Hexadecimal (base 16) | 7B |
| Base 3 | 11120 |
| As time | 123 seconds = 2 min 3 s |
Is 123 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 (123 ÷ 3 = 41) | 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 | No (remainder 3) | 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 3) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 6) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 3) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 2) | A number is divisible by 11 if the alternating sum of the digits is a multiple of 11. |
| 12 | No (remainder 3) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 123 a prime number?
No. 123 = 3 × 41, so it is divisible by 3.
What are the factors of 123?
1, 3, 41, 123.
What is 123 in binary?
1111011 (hexadecimal 7B, octal 173).
What is the square root of 123?
About 11.0905.
What is 123 in Roman numerals?
CXXIII.
Is 123 divisible by 3?
Yes. Its digits add up to 6, a multiple of 3.
What is special about the number 123?
123 is a semiprime: 3 × 41, the product of two primes.