Prime Numbers in PHP

Prime numbers are having only two factors, one is 1 and other one is the number itself.
These are the first 5 prime numbers 2, 3, 5, 7, 11
Prime numbers are divisible by exactly two natural numbers, 1 and the number itself.
Checking and listing all prime numbers in PHP by using loop and form to take user inputs

Checking numbers

Any number we can check if it is Prime number or not .
$n1=18;
$flag=0;
for($i=2;$i<=($n1/2); $i++){
	if($n1%$i == 0 ){
	$flag=1;
	break;
	}
}

if($flag==0){
	echo  "$n1 is a prime number " ;
}else{
	echo  "$n1 is NOT a prime number " ;
}	
Output
18 is NOT a prime number

Sticky form to take user input

We will ask user to enter any number in a sticky form and then display the number is prime number or not.
is a prime number
$n1=$_POST['n1']; // change this number 
echo "<form method=POST action=''>
<input type=text name=n1 value='$n1'>
<input type=Submit value=submit></form>";
$flag=0;
for($i=2;$i<=($n1/2); $i++){
	if($n1%$i == 0 ){
	$flag=1;
	break;
	}
}

if($flag==0){
	echo  "$n1 is a prime number " ;
}else{
	echo  "$n1 is NOT a prime number " ;
}	

Listing all prime numbers

We will loop through a range of numbers and check and list of all the prime numbers. ( All prime numbers less than 100 )
for($j=1;$j<=100;$j++){
$n1=$j;	
$flag=0;
for($i=2;$i<=($n1/2); $i++){
	if($n1%$i == 0 ){
	$flag=1;
	break;
	}
}

if($flag==0){
	echo  "$n1 , " ;
}	
}
Output is here
1 , 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 ,


Introduction to PHP Factorial of a number Sum of Digits of a number
Armstrong number Strong number
Basic Codes Check the string or number is Palindrome or not in PHP

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