The number 129
129 is a binary palindrome (10000001). Its prime factorisation is 3 × 43. Divisors (4): 1, 3, 43, 129.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 129: a binary palindrome (10000001); a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 3 × 43, the product of two primes.
- 2
129 is composite. Its prime factorisation is
- 3
The divisors add up to 176; without 129 itself that is 47, so 129 is deficient (47 is less than 129). Euler's totient φ(129) = 84 numbers up to 129 share no factor with it.
- 4
The digits of 129 add up to 12, and repeating that until one digit is left gives the digital root 3. The Collatz sequence (halve if even, else 3n+1) takes 121 steps to reach 1.
LaTeX source of the formulas on this page
\[ 129 = 3 \times 43 \]
129 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 176 |
| Euler totient φ(n) | 84 |
| Square | 16641 |
| Cube | 2146689 |
| Square root | 11.357817 |
| Digit sum / digital root | 12 / 3 |
| Collatz steps to 1 | 121 |
| Scientific notation | 1.29 × |
129 in other forms
| Form | Value |
|---|---|
| In words | one hundred and twenty-nine |
| Roman numerals | CXXIX |
| Binary (base 2) | 10000001 |
| Octal (base 8) | 201 |
| Hexadecimal (base 16) | 81 |
| Base 3 | 11210 |
| As time | 129 seconds = 2 min 9 s |
Is 129 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 (129 ÷ 3 = 43) | 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 4) | 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 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 1) | 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 9) | A number is divisible by 10 if the last digit is 0. |
| 11 | No (remainder 8) | 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 129 a prime number?
No. 129 = 3 × 43, so it is divisible by 3.
What are the factors of 129?
1, 3, 43, 129.
What is 129 in binary?
10000001 (hexadecimal 81, octal 201).
What is the square root of 129?
About 11.3578.
What is 129 in Roman numerals?
CXXIX.
Is 129 divisible by 3?
Yes. Its digits add up to 12, a multiple of 3.
What is special about the number 129?
129 is a binary palindrome (10000001); a happy number: repeatedly adding the squares of its digits reaches 1; a semiprime: 3 × 43, the product of two primes.