Dear Anonymous, It's very simple. In every iteration the $a receives the earlier value of $b...that's the trick. Bye the way, u can see my ealier attempt, which had one serious mistake... that can be rewritten to give the desired result. See:

$a=1;
$b=1;

while($a <=200)
    {$c=$a+$b;
     print("$a\n$b\n$c\n");
    $a=$b+$c;
    $b=$c+$a;
    }
[download]

Thanks.