Would have posted this earlier but just noticed it. Quento is currently free due to AppGratis and it's a lovely math based puzzle where you have to add numbers that equal a certain number, but only by using the number indicated. Short and sweet too.
You can get it here: https://play.google.com/store/apps/details?id=nl.q42.quento
You can get it here: https://play.google.com/store/apps/details?id=nl.q42.quento