Paul Erdos was an amazing and prolific mathematician whose life as a world-wandering numerical nomad was legendary. He published almost 1500 scholarly papers before his death in 1996, and he probably thought more about math problems than anyone in history. Like a traveling salesman offering his thou[...]

Number theory - the branch of mathematics which studies the properties of the integers - has interesting and quite varied problems, sometimes impossibly difficult ones. The authors have gathered problems from various topics in number theory that they find beautiful, intriguing and instructive.[...]

Most people think of mathematicians as solitary, working away in isolation. And, it's true, many of them do. But Paul Erdos never followed the usual path. At the age of four, he could ask you when you were born and then calculate the number of seconds you had been alive in his head. But he didn't le[...]