Ian Stewart's recent books include (with Terry Pratchett and Jack Cohen) The Science of Discworld IV and (published by Profile) 17 Equations that Changed the World, The Great Mathematical Problems, Professor Stewart's Casebook of Mathematical Mysteries and Calculating the Cosmos. His app, Incredible Numbers, was published jointly by Profile and Touch Press in 2014.
Praise for the app - starred review 'TouchPress and Stewart offer eight challenging dives into mathematical theory and practice for readers not intimidated by complex formulas and brain-bending concepts... The author swims easily through the sometimes turbid sea of numbers, and the clean graphics, sharp photos and well-designed features that accompany his lucid explanations will help draw readers along in his wake. Kirkus Britain's most brilliant and prolific populariser of mathematics -- Alex Bellos