<?php

function calc( $num ){

    for( $i = 1; $i < $num; $i++ ){
       $fark = $num - $i;
        //echo $fark;
        echo strval("$i + $fark")."<br>";
    }
    
}

calc( 15 );

?>

1 + 14
2 + 13
3 + 12
4 + 11
5 + 10
6 + 9
7 + 8
8 + 7
9 + 6
10 + 5
11 + 4
12 + 3
13 + 2
14 + 1