I've written out the Regex for divisibility by 3 before, it's a bit of a beast. I've had a blog post half-finished for ages where I talked about just this thin

I've written out the Regex for divisibility by 3 before, it's a bit of a beast. I've had a blog post half-finished for ages where I talked about just this thing, but I never got around to actually computing the re for divisibility by 7. Maybe this will provide the impetus...