<?php$numbers = [2, 3, 5, 7, 11, 13, 17];$str = ""; $len = count($numbers);for ($i = 0; $i < $len; $i++) { $str .= ($str == "" ? "" : "; ") . $numbers[$i];}//str is "2; 3; 5; 7; 11; 13; 17"echo $str;