A science fiction novel about artificial intelligence, politics, cellular automata, climate change and alternate universes that takes place in India of 2047. Math plays only a very small role in this complex and imaginative novel, but enough for me to include it in this list of "mathematical fiction". There is, of course, much more that can be said about this winner of the British Science Fiction Association's award for Best Novel...but this site is not the right place for it.
The main source of math in this novel is the character of Lisa Durnau, a scientist whom we see kidnapped by NASA and shown a bizarre, ancient cellular automata hidden inside an asteroid in our solar system. At one point, in a flashback, we share with her the thrill of mathematical discovery. This is one of my favorite things in mathematical fiction since it is a part of mathematics that few get to really enjoy, not only the thrill of figuring something out with your own mind the the pride of knowing that you are the first person to have ever done so.
(quoted from River of Gods)
She sat at her table shuddering with shame and tears and the certainty that her career was over, she could not do this thing, she didn't know what they meant. Her bladder called ten minutes before her train. She sat in the cubicle, jeans around her knees, trying not to sob out loud because the acoustics of London station toilets would take it and amplify it so everyone could hear.
And then she saw it. She could not say what it was she saw, staring at the cubicle door, there was no shape, no form, no words or theorems. But it was there, whole and unimaginably beautiful. It was simple. It was so simple. Lisa Durnau burst from the cubicle, rushed to the Paperchase store, bought a pad and a big marker. Then she ran for her train. She never made it. Somewhere between the fifth and sith carriages, it hit her like lightening. She knew exactly what she had to do. She knelt sobbing on the platform while her shaking hands tried to jam down equations. Ideas poured through her. She was hardwired to the cosmos. The evening shift detoured around her, not staring. It's all right, she wanted to say. It's so all right.

The explanation of her theory involves lots of name dropping:
 "CalabiYau Manifolds": Eugenio Calabi and ShingTung Yau are real mathematicians who conjectured and proved (respectively) a theorem about compact Kähler manifolds. This sounds pretty obscure, and you would not think their names would be quite so common in science fiction novels as they are. However, as it turns out, these CalabiYau manifolds play an important role in string theories of quantum gravity. I guess they must have a "ring" to them because you can find them in quite a few stories these days.
 "WolframFriedkin Conjecture": Again, these are two real mathematicians. Steve Wolfram was a mathematician working on cellular automata when he founded a company that makes mathematical computer software and became a millionaire. Ed Friedkin is a (presumably less wealthy) researcher on cellular automata as well. I am not aware that there is any real conjecture bearing their name, but if you know that I am mistaken about this I would appreciate hearing from you!
 "Atiyah Ladder Effect": Sir Michael Atiyah is one of my personal favorite mathematicians, and so it is nice to see his name mentioned, but I am not aware that there is any such effect named after him. (Again, let me know if I'm wrong about this!)
Zeropoint energy (getting energy from universes that have a higher vacuum energy than ours) and the concept of a Boltzmon are also key to the novel.
McDonald is one of my favorite authors (I loved "Out on Blue Six"!) and his latest certainly does not disappoint. Mindblowing ideas and interesting cultural references are embedded in a satisfying but complex plot. My only complaint is that there was too much sex and violence and not enough math...but then few readers are likely to agree with me on that point. 