The Case of the Flying Hands, by Harry Stephen Keeler (epub/Kindle/pdf)

Quiribus Brown, 7½ foot tall hick from the sticks, wants nothing more than to be a detective. But not just any kind of detective—he wants to be a solver of mysteries with a mathematical bent, and in this posthumously-published novel Quiribus comes up against three of the most puzzling mathematical mysteries ever dreamed up in the crazy, fertile imagination of Harry Stephen Keeler. Author/editor Francis M. Nevins supplies a detailed introduction about Keeler’s most unusual character, a giant detective with a brain full of numbers.