Is 255 a prime number?

It is possible to find out using mathematical methods whether a given integer is a prime number or not.

For 255, the answer is: No, 255 is not a prime number.

The list of all positive divisors (i.e., the list of all integers that divide 255) is as follows: 1, 3, 5, 15, 17, 51, 85, 255.

For 255 to be a prime number, it would have been required that 255 has only two divisors, i.e., itself and 1.

Find out more:

What is a prime number?

Actually, one can immediately see that 255 cannot be prime, because 5 is one of its divisors: indeed, a number ending with 0 or 5 has necessarily 5 among its divisors. The last digit of 255 is 5, so it is divisible by 5 and is therefore not prime.

As a consequence:

255 is a multiple of 1
255 is a multiple of 3
255 is a multiple of 5
255 is a multiple of 15
255 is a multiple of 17
255 is a multiple of 51
255 is a multiple of 85

For 255 to be a prime number, it would have been required that 255 has only two divisors, i.e., itself and 1.

Is 255 a deficient number?

Yes, 255 is a deficient number, that is to say 255 is a natural number that is strictly larger than the sum of its proper divisors, i.e., the divisors of 255 without 255 itself (that is 1 + 3 + 5 + 15 + 17 + 51 + 85 = 177).

Parity of 255

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

Find out more:

What is an even number?

Is 255 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 255 is about 15.969.

Thus, the square root of 255 is not an integer, and therefore 255 is not a square number.

What is the square number of 255?

The square of a number (here 255) is the result of the product of this number (255) by itself (i.e., 255 × 255); the square of 255 is sometimes called "raising 255 to the power 2", or "255 squared".

The square of 255 is 65 025 because 255 × 255 = 255² = 65 025.

As a consequence, 255 is the square root of 65 025.

Number of digits of 255

255 is a number with 3 digits.

What are the multiples of 255?

The multiples of 255 are all integers evenly divisible by 255, that is all numbers such that the remainder of the division by 255 is zero. There are infinitely many multiples of 255. The smallest multiples of 255 are:

0: indeed, 0 is divisible by any natural number, and it is thus a multiple of 255 too, since 0 × 255 = 0
255: indeed, 255 is a multiple of itself, since 255 is evenly divisible by 255 (we have 255 / 255 = 1, so the remainder of this division is indeed zero)
510: indeed, 510 = 255 × 2
765: indeed, 765 = 255 × 3
1 020: indeed, 1 020 = 255 × 4
1 275: indeed, 1 275 = 255 × 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 255). 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 15.969). 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 255

Preceding numbers: …253, 254
Following numbers: 256, 257…

Nearest numbers from 255

Preceding prime number: 251
Following prime number: 257