Is 155 a prime number? What are the divisors of 155?

## Parity of 155

155 is an odd number, because it is not evenly divisible by 2.

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## Is 155 a perfect square number?

A number is a perfect square (or a square number) if its square root is an integer; that is to say, it is the product of an integer with itself. Here, the square root of 155 is about 12.450.

Thus, the square root of 155 is not an integer, and therefore 155 is not a square number.

## What is the square number of 155?

The square of a number (here 155) is the result of the product of this number (155) by itself (i.e., 155 × 155); the square of 155 is sometimes called "raising 155 to the power 2", or "155 squared".

The square of 155 is 24 025 because 155 × 155 = 1552 = 24 025.

As a consequence, 155 is the square root of 24 025.

## Number of digits of 155

155 is a number with 3 digits.

## What are the multiples of 155?

The multiples of 155 are all integers evenly divisible by 155, that is all numbers such that the remainder of the division by 155 is zero. There are infinitely many multiples of 155. The smallest multiples of 155 are:

• 0: indeed, 0 is divisible by any natural number, and it is thus a multiple of 155 too, since 0 × 155 = 0
• 155: indeed, 155 is a multiple of itself, since 155 is evenly divisible by 155 (we have 155 / 155 = 1, so the remainder of this division is indeed zero)
• 310: indeed, 310 = 155 × 2
• 465: indeed, 465 = 155 × 3
• 620: indeed, 620 = 155 × 4
• 775: indeed, 775 = 155 × 5
• etc.

## How to determine whether an integer is a prime number?

To determine the primality of a number, several algorithms can be used. The most naive technique is to test all divisors strictly smaller to the number of which we want to determine the primality (here 155). First, we can eliminate all even numbers greater than 2 (and hence 4, 6, 8…). Then, we can stop this check when we reach the square root of the number of which we want to determine the primality (here the square root is about 12.450). Historically, the sieve of Eratosthenes (dating from the Greek mathematics) implements this technique in a relatively efficient manner.

More modern techniques include the sieve of Atkin, probabilistic algorithms, and the cyclotomic AKS test.

## Numbers near 155

• Preceding numbers: …153, 154
• Following numbers: 156, 157

### Nearest numbers from 155

• Preceding prime number: 151
• Following prime number: 157
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