The Roman numeral X represents the number 10, and since Panther is the third iteration of OS X, ten plus three equals 13! Also, a Panther is a black cat! It’s bad luck. Get rid of it. Get 10.4 Tiger, and move on to a luckier life.
If you make the switch today, perhaps you can successfully cancel out the bad luck of the day, you superstitious weirdo.