Looks very nice. However it took me a while to figure out why I kept getting error. It wasn't obvious to me that you are required to enter prime numbers only. M

Looks very nice. However it took me a while to figure out why I kept getting error. It wasn't obvious to me that you are required to enter prime numbers only. Maybe consider dropping this constraint? Also, might want to disable text selection via css because I kept selecting the numbers on the button on my phone.