Check if a number is prime or not.

Isprime function return a boolean (true or false) depend on the number is prime or not.

Isprime function return a boolean (true or false) depend on the number is prime or not.

* Put a number in every line.

A natural number $n$ is a prime number if and only if had exactely $2$ divisors.

The first prime numbers less than $100$:

The first prime numbers less than $100$:

$\displaystyle{2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97}$

A composite number $n$ has a divisor $d$ verify : $2 \leq d \leq \sqrt{n}$.

Then to check a number $n$ if it's prime or not we should try the divisibility of $n$ by prime numbers less than $\sqrt{n}$.

This method is useful only with small numbers, if we have large numbers we should use other algorithms like Millerâ€“Rabin primality test.

Then to check a number $n$ if it's prime or not we should try the divisibility of $n$ by prime numbers less than $\sqrt{n}$.

This method is useful only with small numbers, if we have large numbers we should use other algorithms like Millerâ€“Rabin primality test.

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