- Output for 7.1.25 - 7.1.28, 7.2.0 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.7
- array ( 4 => 5, 6 => 7, 7 => 8, )
<?php
$arr = [1,2,3,4,6,9]; // your array
$range = range(min($arr), max($arr));
var_export(array_diff($range, $arr));