I haven't tried this yet, but Stanford mathematician Keith Devlin's new game company has put out a free math app emphasizing conceptual mathematics, in this particular game integer partitions and Diophantine equations.

Wuzzit Trouble for iOS
puzzle game suitable for ages 8-80

Here's the website for Inner Tube Games that explains more about the game:
http://innertubegames.net/index.html

Thank you so much for posting this!