## Is 27 a prime number?

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

For 27, the answer is: No, 27 is not a prime number.

The list of all positive divisors (i.e., the list of all integers that divide 27) is as follows: 1, 3, 9, 27.

To be 27 a prime number, it would have been required that 27 has only two divisors, i.e., itself and 1.

As a consequence:

To be 27 a prime number, it would have been required that 27 has only two divisors, i.e., itself and 1.

## Is 27 a deficient number?

Yes, 27 is a deficient number, that is to say 27 is a natural number that is strictly larger than the sum of its proper divisors, i.e., the divisors of 27 without 27 itself (that is 1 + 3 + 9 = 13).

## Parity of 27

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

## Is 27 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 27 is about 5.196.

Thus, the square root of 27 is not an integer, and therefore 27 is not a square number.

## What is the square number of 27?

The square of a number (here 27) is the result of the product of this number (27) by itself (i.e., 27 × 27); the square of 27 is sometimes called "raising 27 to the power 2", or "27 squared".

The square of 27 is 729 because 27 × 27 = 27^{2} = 729.

As a consequence, 27 is the square root of 729.

## Number of digits of 27

27 is a number with 2 digits.

## What are the multiples of 27?

The multiples of 27 are all integers evenly divisible by 27, that is all numbers such that the remainder of the division by 27 is zero. There are infinitely many multiples of 27. The smallest multiples of 27 are:

- 0: indeed, 0 is divisible by any natural number, and it is thus a multiple of 27 too, since 0 × 27 = 0
- 27: indeed, 27 is a multiple of itself, since 27 is evenly divisible by 27 (we have 27 / 27 = 1, so the remainder of this division is indeed zero)
- 54: indeed, 54 = 27 × 2
- 81: indeed, 81 = 27 × 3
- 108: indeed, 108 = 27 × 4
- 135: indeed, 135 = 27 × 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 27). 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 5.196). 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.