The number 128
128 is a power of 2 (). Its prime factorisation is . Divisors (8): 1, 2, 4, 8, 16, 32, 64, 128.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 128: a power of 2 ().
- 2
128 is composite. Its prime factorisation is
- 3
The divisors add up to 255; without 128 itself that is 127, so 128 is deficient (127 is less than 128). Euler's totient φ(128) = 64 numbers up to 128 share no factor with it.
- 4
The digits of 128 add up to 11, and repeating that until one digit is left gives the digital root 2. The Collatz sequence (halve if even, else 3n+1) takes 7 steps to reach 1.
LaTeX source of the formulas on this page
\[ 128 = 2^{7} \]128 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 8 |
| Sum of divisors | 255 |
| Euler totient φ(n) | 64 |
| Square | 16384 |
| Cube | 2097152 |
| Square root | 11.313708 (= 8√2) |
| Digit sum / digital root | 11 / 2 |
| Collatz steps to 1 | 7 |
| Scientific notation | 1.28 × |
| Perfect power |
128 in other forms
| Form | Value |
|---|---|
| In words | one hundred and twenty-eight |
| Roman numerals | CXXVIII |
| Binary (base 2) | 10000000 |
| Octal (base 8) | 200 |
| Hexadecimal (base 16) | 80 |
| Base 3 | 11202 |
| As time | 128 seconds = 2 min 8 s |
Is 128 divisible by 2 to 12?
| Divisor | Answer | Rule |
|---|---|---|
| 2 | Yes (128 ÷ 2 = 64) | A number is divisible by 2 if the last digit is even (0, 2, 4, 6, 8). |
| 3 | No (remainder 2) | A number is divisible by 3 if the digits add up to a multiple of 3. |
| 4 | Yes (128 ÷ 4 = 32) | 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 2) | 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 | Yes (128 ÷ 8 = 16) | A number is divisible by 8 if the last three digits make a multiple of 8. |
| 9 | No (remainder 2) | A number is divisible by 9 if the digits add up to a multiple of 9. |
| 10 | No (remainder 8) | 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 8) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 128 a prime number?
No. 128 = , so it is divisible by 2.
What are the factors of 128?
1, 2, 4, 8, 16, 32, 64, 128.
What is 128 in binary?
10000000 (hexadecimal 80, octal 200).
What is the square root of 128?
About 11.3137, exactly 8√2.
What is 128 in Roman numerals?
CXXVIII.
Is 128 divisible by 3?
No. Its digits add up to 11, which is not a multiple of 3.
What is special about the number 128?
128 is a power of 2 ().