Is 643 a prime number? What are the divisors of 643?

## Parity of 643

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

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## Is 643 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 643 is about 25.357.

Thus, the square root of 643 is not an integer, and therefore 643 is not a square number.

Anyway, 643 is a prime number, and a prime number cannot be a perfect square.

## What is the square number of 643?

The square of a number (here 643) is the result of the product of this number (643) by itself (i.e., 643 × 643); the square of 643 is sometimes called "raising 643 to the power 2", or "643 squared".

The square of 643 is 413 449 because 643 × 643 = 6432 = 413 449.

As a consequence, 643 is the square root of 413 449.

## Number of digits of 643

643 is a number with 3 digits.

## What are the multiples of 643?

The multiples of 643 are all integers evenly divisible by 643, that is all numbers such that the remainder of the division by 643 is zero. There are infinitely many multiples of 643. The smallest multiples of 643 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 643). 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 25.357). 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 643

• Preceding numbers: …641, 642
• Following numbers: 644, 645

### Nearest numbers from 643

• Preceding prime number: 641
• Following prime number: 647
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