Nick O'Donohoe's The Magic and the Healing, Under the Healing Sign, and The Healing of Crossroads. Thank you. I'd forgotten those completely; and I read them, too. I think they came out in the mid-'90's.

If Mathemagic is what it sounds like, I didn't realize it was a novel—I just remember a set of short stories in various Chicks in Chainmail anthologies. Neat.