Dividing a integer equally in X parts

Here's the algorithm you're looking for; it evenly spreads an integer N over K cells:

for i = 0 to K
    array[i] = N / K    # integer division

# divide up the remainder
for i = 0 to N mod K
    array[i] += 1

Try this code

<?php
$num = 400;
$val = floor($num/24);

for($i=0;$i<24;$i++) {
    $arr[$i] = $val;
}

$arr[0] += $num - array_sum($arr);
?>