PHP：如何计算最大值 排列数

Let say I have some variables containing different numbers:

$element_a =1;
$element_b =1;
$element_c =7;
$element_d =8;
$element_e =15;
$element_f =7;
$element_g =7;

and the script choose a random number for each var:

$element_a = rand (1, $element_a);
$element_b = rand (1, $element_b);
$element_c = rand (1, $element_c);
$element_d= rand (1, $element_d);
$element_e= rand (1, $element_e);
$element_f= rand (1, $element_f);
$element_g= rand (1, $element_g);

and now, all this elements generate a situation,

how can i calculate how many different situations are possible?