The number 155
155 is a composite number with 4 divisors. Its prime factorisation is 5 × 31. Divisors (4): 1, 5, 31, 155.
Pick any whole number from 1 to 100,000.
How to work it out
- 1
What is special about 155: a semiprime: 5 × 31, the product of two primes.
- 2
155 is composite. Its prime factorisation is
- 3
The divisors add up to 192; without 155 itself that is 37, so 155 is deficient (37 is less than 155). Euler's totient φ(155) = 120 numbers up to 155 share no factor with it.
- 4
The digits of 155 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 85 steps to reach 1.
LaTeX source of the formulas on this page
\[ 155 = 5 \times 31 \]
155 at a glance
| Property | Value |
|---|---|
| Type | composite |
| Number of divisors | 4 |
| Sum of divisors | 192 |
| Euler totient φ(n) | 120 |
| Square | 24025 |
| Cube | 3723875 |
| Square root | 12.449900 |
| Digit sum / digital root | 11 / 2 |
| Collatz steps to 1 | 85 |
| Scientific notation | 1.55 × |
155 in other forms
| Form | Value |
|---|---|
| In words | one hundred and fifty-five |
| Roman numerals | CLV |
| Binary (base 2) | 10011011 |
| Octal (base 8) | 233 |
| Hexadecimal (base 16) | 9B |
| Base 3 | 12202 |
| As time | 155 seconds = 2 min 35 s |
Is 155 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 2) | 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 (155 ÷ 5 = 31) | A number is divisible by 5 if the last digit is 0 or 5. |
| 6 | No (remainder 5) | A number is divisible by 6 if it is divisible by both 2 and 3. |
| 7 | No (remainder 1) | 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 2) | 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 11) | A number is divisible by 12 if it is divisible by both 3 and 4. |
Questions
Is 155 a prime number?
No. 155 = 5 × 31, so it is divisible by 5.
What are the factors of 155?
1, 5, 31, 155.
What is 155 in binary?
10011011 (hexadecimal 9B, octal 233).
What is the square root of 155?
About 12.4499.
What is 155 in Roman numerals?
CLV.
Is 155 divisible by 3?
No. Its digits add up to 11, which is not a multiple of 3.
What is special about the number 155?
155 is a semiprime: 5 × 31, the product of two primes.