Roger B Nelsen 
Nuggets of Number Theory [PDF ebook] 

Nuggets of Number Theory will attract fans of visual thinking, number theory, and surprising connections. This book contains hundreds of visual explanations of results from elementary number theory. Figurate numbers and Pythagorean triples feature prominently, of course, but there are also proofs of Fermat’s Little and Wilson’s Theorems. Fibonacci and perfect numbers, Pell’s equation, and continued fractions all find visual representation in this charming collection. It will be a rich source of visual inspiration for anyone teaching, or learning, number theory and will provide endless pleasure to those interested in looking at number theory with new eyes. Author Roger Nelsen is a long-time contributor of "Proofs Without Words" in the MAA’s Mathematics Magazine and College Mathematics Journal. This is his twelfth book with MAA Press.