Reminded me of The Traitor Baru Cormorant in themes, but while I enjoyed that one greatly, I mostly wanted this one to be over except for a little bit at the end. So perhaps I'll enjoy the sequel more?

The math stuff didn't quite work for me. Seemed it could have gone in a more sapir-whorf direction and been about different mathematical systems influencing how people think, or perhaps that was really the case and I missed it? Instead it often felt like magic/numerology for its own sake.

(One explanation for the calinderical math stuff could be super far-future computer systems, but then there was a bit where the 67 snake crypto was seeded by "the irregular time between keystrokes" and a network time server, which while plausible for the crypto of some decrepit empire, makes it less sophisticated than current-day cryptosystems.)

Despite all that, I can't see rating it less than 3 stars, and since I still find myself thinking about it, 4 seems best.