<?php $input = '1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39';
Standard input is empty
Array ( [1] => 1 [3] => 1 [5] => 1 [7] => 1 [9] => 1 [11] => 1 [13] => 1 [15] => 1 [17] => 1 [19] => 1 [21] => 1 [23] => 1 [25] => 1 [27] => 1 [29] => 1 [31] => 1 [33] => 1 [35] => 1 [37] => 1 [39] => 1 )