[martinclayton]

Hours of fun (stimulation?) to be had...

Try these shapes: 100x113, then 100x114, then 100x115, the "patterns" swing from slant down, to vertical, to slant up.

I'd love this (even more) with some animation and colo(u)r options.

[susam]

This was just a quick experiment I put together last night in my free time, so the tool is quite bare bones. If you're on a desktop browser and don't mind opening the developer tools console, you can run this little snippet to animate the grid:

  cols.value = 1n; setInterval(() => {cols.value++; readInput()}, 250);

[AnotherGoodName]

This is also basically the most trivial proof that primes are infinite. If you think you've discovered all the primes, just multiply all those primes together and add or subtract 1. You now have a new number that shares no factors with those primes.