Is 855 a prime number?

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

For 855, the answer is: No, 855 is not a prime number.

The list of all positive divisors (i.e., the list of all integers that divide 855) is as follows: 1, 3, 5, 9, 15, 19, 45, 57, 95, 171, 285, 855.

For 855 to be a prime number, it would have been required that 855 has only two divisors, i.e., itself and 1.

Find out more:

What is a prime number?

Actually, one can immediately see that 855 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 855 is 5, so it is divisible by 5 and is therefore not prime.

As a consequence:

855 is a multiple of 1
855 is a multiple of 3
855 is a multiple of 5
855 is a multiple of 9
855 is a multiple of 15
855 is a multiple of 19
855 is a multiple of 45
855 is a multiple of 57
855 is a multiple of 95
855 is a multiple of 171
855 is a multiple of 285

For 855 to be a prime number, it would have been required that 855 has only two divisors, i.e., itself and 1.

Is 855 a deficient number?

Yes, 855 is a deficient number, that is to say 855 is a natural number that is strictly larger than the sum of its proper divisors, i.e., the divisors of 855 without 855 itself (that is 1 + 3 + 5 + 9 + 15 + 19 + 45 + 57 + 95 + 171 + 285 = 705).

Parity of 855

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

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What is an even number?

Is 855 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 855 is about 29.240.

Thus, the square root of 855 is not an integer, and therefore 855 is not a square number.

What is the square number of 855?

The square of a number (here 855) is the result of the product of this number (855) by itself (i.e., 855 × 855); the square of 855 is sometimes called "raising 855 to the power 2", or "855 squared".

The square of 855 is 731 025 because 855 × 855 = 855² = 731 025.

As a consequence, 855 is the square root of 731 025.

Number of digits of 855

855 is a number with 3 digits.

What are the multiples of 855?

The multiples of 855 are all integers evenly divisible by 855, that is all numbers such that the remainder of the division by 855 is zero. There are infinitely many multiples of 855. The smallest multiples of 855 are:

0: indeed, 0 is divisible by any natural number, and it is thus a multiple of 855 too, since 0 × 855 = 0
855: indeed, 855 is a multiple of itself, since 855 is evenly divisible by 855 (we have 855 / 855 = 1, so the remainder of this division is indeed zero)
1 710: indeed, 1 710 = 855 × 2
2 565: indeed, 2 565 = 855 × 3
3 420: indeed, 3 420 = 855 × 4
4 275: indeed, 4 275 = 855 × 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 855). 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 29.240). 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 855

Preceding numbers: …853, 854
Following numbers: 856, 857…

Nearest numbers from 855

Preceding prime number: 853
Following prime number: 857