Daily UI Design Challenge #004 Calculator

To be honest, a calculator mmmm, doesn´t mean any challenge, at least at a first view. Anyway, I´ll be followin:

• CollectUI Calculators
• Pttrns
• Dribbble

Don´t find much of this. These ones I like:

So I made a grid, then put some grey color (there´s one mistake in a cell, can you see it?) Finally thought of a Mondrian Calculator, I think it could be also a game, like Simon game in example.