Pedant: "Power of 2 minus 1" is a more precise match than "prime" methinks. (1 year, 3 months ago)
Milo: Far too ambiguous. There should only be one possible answer to each group.
Answer to second should just be "perfect".
Answer to last one could just as easily be numbers in film titles. (1 year, 6 months ago)
MFSM: Too easy to group the numbers and words. (5 years, 12 months ago)
Syrinx: Typing in Perfect gives an "incorrect" response. Annoying! (6 years, 10 months ago)
tabstop: Cute, but that unfortunately makes it pretty easy. (7 years, 2 months ago)