64*64 = 4096
Screen resolutions of less than 64*64 are permitted.
Could I have a resolution of, for example, 52*78 - since 4056 is less than 4096?

It's pedantry I know, I'm just curious :)

Not as per the generally understood rules of the jam. You could try it though, explain your reasoning, and the voters might go easy on you! :)

I thought it would be a grey-area thing - thanks for clarifying!

I doubt I will try anything like this, but messing around with the format a little could be fun. I also thought a different resolution might work better for a mobile game with no on-screen controls.

While that's an interesting idea... the resolution is kind of the entire point. I'd definitely be interested in a "you have this many pixels to work with in whatever configuration you want" premise, though; that could be a great jam by itself.

Well, my 2016 LRJ entry ended up on mobile after the jam , at which point I just increased the resolution width. I guess my advice would be to do the simplest, clearest thing during the jam, than change it for specific platforms after.