Is 400 a prime number? What are the divisors of 400?

## Parity of 400

400 is an even number, because it is evenly divisible by 2: 400 / 2 = 200.

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## Is 400 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 400 is 20.

Therefore, the square root of 400 is an integer, and as a consequence 400 is a perfect square.

As a consequence, 20 is the square root of 400.

## What is the square number of 400?

The square of a number (here 400) is the result of the product of this number (400) by itself (i.e., 400 × 400); the square of 400 is sometimes called "raising 400 to the power 2", or "400 squared".

The square of 400 is 160 000 because 400 × 400 = 4002 = 160 000.

As a consequence, 400 is the square root of 160 000.

## Number of digits of 400

400 is a number with 3 digits.

## What are the multiples of 400?

The multiples of 400 are all integers evenly divisible by 400, that is all numbers such that the remainder of the division by 400 is zero. There are infinitely many multiples of 400. The smallest multiples of 400 are:

## 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 400). 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 20). 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 400

• Preceding numbers: …398, 399
• Following numbers: 401, 402

### Nearest numbers from 400

• Preceding prime number: 397
• Following prime number: 401
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