Metta - Prime Number

; put you code here
( = (largest_prime_factor $x $d)
    (
        case $x
        (
            ($_ (
                (if (< $x 1) (nil) ())
                (if (< $x (* $d $d)) ($x) ())
                (if (== 0 (% $x $d)) (largest_prime_factor (/ $x $d) $d) ())
                ( largest_prime_factor $x (+ $d 1) )
            )   
            )
        )
    )
)

! (largest_prime_factor 5 2)