List all the prime numbers less than or equal to a given integer n in PHP

prime_number_list.php

<?php
/**
 * @author Bishwanath Jha <bishwanathkj@gmail.com>
 * Give the nth number as input and it will return all prime numbers less than or equal to that number
 */
function GetPrimeNumberList($num) {
	if ($num == 1) {
		return $num;
	}

	$list = [1];
	for($i = 2; $i <= $num; $i++) {
		for($j = 2; $j < $i/2; $j++) {
			if($i % $j == 0) break;
		}
		
		if($j == $i ) $list[] = $i;
	}

	return $list;
}

print_r(GetPrimeNumberList(20));

/**
Output:
Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 5
    [4] => 7
    [5] => 11
    [6] => 13
    [7] => 17
    [8] => 19
) */