Is 128 a prime number? What are the divisors of 128?

## Parity of 128

128 is an even number, because it is evenly divisible by 2: 128 / 2 = 64.

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## Is 128 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 128 is about 11.314.

Thus, the square root of 128 is not an integer, and therefore 128 is not a square number.

## What is the square number of 128?

The square of a number (here 128) is the result of the product of this number (128) by itself (i.e., 128 × 128); the square of 128 is sometimes called "raising 128 to the power 2", or "128 squared".

The square of 128 is 16 384 because 128 × 128 = 1282 = 16 384.

As a consequence, 128 is the square root of 16 384.

## Number of digits of 128

128 is a number with 3 digits.

## What are the multiples of 128?

The multiples of 128 are all integers evenly divisible by 128, that is all numbers such that the remainder of the division by 128 is zero. There are infinitely many multiples of 128. The smallest multiples of 128 are:

• 0: indeed, 0 is divisible by any natural number, and it is thus a multiple of 128 too, since 0 × 128 = 0
• 128: indeed, 128 is a multiple of itself, since 128 is evenly divisible by 128 (we have 128 / 128 = 1, so the remainder of this division is indeed zero)
• 256: indeed, 256 = 128 × 2
• 384: indeed, 384 = 128 × 3
• 512: indeed, 512 = 128 × 4
• 640: indeed, 640 = 128 × 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 128). 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 11.314). 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 128

• Preceding numbers: …126, 127
• Following numbers: 129, 130

### Nearest numbers from 128

• Preceding prime number: 127
• Following prime number: 131
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