<?php
// The magic three sequence is the sum of the previous three values minus 1.
//
// 0,1,1,1,2,3,5,9,16,
function magicThree($n) {
if ($n < 1) return;
$n--; // To an index;
$s = array(0,1,1,1);
if ($n > 3) {
for ($i = 4; $i <= $n; $i++) {
$s[$i] = $s[$i-1] + $s[$i-2] + $s[$i-3] - 1;
}
}
print $s[$n];
}
magicThree(7);
?>