<?php

	$dezenas = array("2", "4", "5", "6", "7", "9", "10", "12", "15", "16", "18", "20", "21", "22", "23", "24", "25");
	
	function combinacoesDe($k, $xs){
	        if ($k === 0)
	            return array(array());
	        if (count($xs) === 0)
	            return array();
	        $x = $xs[0];
	        $xs1 = array_slice($xs,1,count($xs)-1);
	        $res1 = combinacoesDe($k-1,$xs1);
	        for ($i = 0; $i < count($res1); $i++) {
	            array_splice($res1[$i], 0, 0, $x);
	        }
	        $res2 = combinacoesDe($k,$xs1);
	        return array_merge($res1, $res2);
	    }
	
	
	print_r(combinacoesDe(15,$dezenas));