Have a bad case of paraskevidekatriaphobia, or fear of Friday the 13th?

The 13th of a month will fall on a Friday more than any other day of the week.  In a 400 year cycle, the 13th of the month will fall on Friday 688 times, just beating Wednesday and Sunday.
-Chapter 13, from the book:

Mathematical Proof of Implausible Ideas

by Julian Havil

Math–the application of reasonable logic to reasonable assumptions–usually produces reasonable results. But sometimes math generates astonishing paradoxes–conclusions that seem completely unreasonable or just plain impossible but that are nevertheless demonstrably true. Did you know that a losing sports team can become a winning one by adding worse players than its opponents? Or that cones can roll unaided uphill? In Nonplussed!–a delightfully eclectic collection of paradoxes from many different areas of math–popular-math writer Julian Havil reveals the math that shows the truth of these and many other unbelievable ideas.

We invite you to read the introduction online:

Available in paperback and e-book.

Also available by Julian Havil
Surprising Solutions to Counterintuitive Conundrums