Interestingly done. Though I found it a bit too easy. If you always memorize the top 5 cards, they usually turn out to fit the sum perfectly. If not you can randomly place any of the bottom 5 until you get a certain minimum and then complete it with the top 5 you've already memorized. So I'd say the main flaw is that, the core gameplay involves memory and luck, which means there isn't any difficulty increase (except in the numbers getting larger) or emergent strategies I can use to create variation.