INCREDIBLE NUMBERS

TouchPress and Stewart offer eight challenging dives into mathematical theory and practice for readers not intimidated by complex formulas and brain-bending concepts.

Floating balloons on the opening screen lead to concise explorations of select topics in areas ranging from “Primes” to “Polygons,” “Infinity” to “Music.” In “Nature,” for instance, Stewart focuses on the discovery of the oddly similar but not identical “golden” and Fibonacci numbers and their occurrences in phenomena from sunflowers to spiral galaxies. Likewise, in “Infinity,” he covers set theory and other efforts to make sense of that concept’s bewildering paradoxes. Throughout, readers can tap highlighted names and special terms throughout to see definitions or biographical sketches. They can also search (with near-certain success) for their own birthdays in the first million digits of pi, create a message Enigma Machine–style in “Secret Codes” and experiment with harmonic intervals in “Music,” among other clever interactive demonstrations. 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. This may tempt even children who tremble at the sight of a square root to take the plunge. (Requires iOS 7.1 and above.) (iPad informational app. 14 & up)