Tough. Learned a lot.

To make it a 4kyu challenge, I suggest to add this test case: (5_599_653, 4_300_533_504)

Brilliant implementation. Can't think of any better way to solve this.

Love this kata.
If anyone can come up with a mathematical solution, I'd be highly interested.

Thanks you for finding the sequence. I wondered what kind of math was underneath this kata.

Turns out to be a math challenge, rather than programming. Very challenging test suite.

I agree.

On one hand it's the temptation and ease of regex, on the other is the temptation of writing a beautifully structured interpreter toolchain

Great kata! Touches a couple of side problems. I learned something.

Implemented a deterministic solution with complexity O(n^3) in Python. Solves 70-by-70 puzzles in <10s on my laptop.

Nice game. This is 5% coding, 95% thinking.

Great kata. Sounds simple, turns out to be very challenging.

Couldn't you copy and paste it here? Having to go to a different kata to see information you need in this one shouldn't be needed. Even more when this is the easier one, and the normal order for doing this should be easier first, harder later, not the other way around.

Thanks.
CONTIGUOUS. There is only one 2 next to 3.