I'd strongly prefer a UX of "Prime" "Composite" buttons, not "yes" "no". And exclude 1; it's special (not-prime for good reasons, but also not composite; Prime

I'd strongly prefer a UX of "Prime" "Composite" buttons, not "yes" "no". And exclude 1; it's special (not-prime for good reasons, but also not composite; Prime vs. Non-Prime isn't as good a test. Plus, treatment of one is largely for definitional reasons and isn't intuitive to non-mathematicians. Fun game, though!