This game is based on multiples of 9. It was the first of a few I uploaded to share some examples of what this script can do.
A 16 card memory game - match the pairs of cards by clicking on them two at a time. Each pair remains visible for 3 seconds if unmatched. Matched pairs disappear.
Obviously, I'm happy for this script to be remixed. There are other Concentration scripts out there if you want to look at other approaches to programming this: (It's a fun project and there are plenty more features that could be added to this type of game)
The earliest example I can find in Scratch is ellieelectron's project: http://scratch.mit.edu/projects/ellieelectrons/105305 - followed by aussieinca's project: http://scratch.mit.edu/projects/aussieinca/284936 and LewsTherrinTelamon'sproject: http://scratch.mit.edu/projects/LewsTherrinTelamon/348904 - greenflash has a project as part of a very interesting portfolio: http://scratch.mit.edu/projects/greenflash/722537 and HamSandwitch678 has a version at: http://scratch.mit.edu/projects/hamsandwitch678/730055
Another version - 1s1s by ScriptTreeSaver http://scratch.mit.edu/projects/ScriptTreeSaver/1707289 was featured on 4 May 2011.
ffred has a very interesting implementation here: http://scratch.mit.edu/projects/ffred/858034
A recent very pretty version by goch is at http://scratch.mit.edu/projects/goch/1797330