Pull any bill out of your wallet. See the dark green numbers on the top-left and top-right corners? Those are serial numbers, and some are more rare than others. If you happen to have paper money with ...

What is your favorite number? For many people, it may be an irrational number such as pi (π), Euler’s number (e) or the square root of 2. Even among the natural numbers (positive integers), there are ...

What is the most bizarre real number that you can imagine? Probably many people think of an irrational number such as pi (π) or Euler’s number. And indeed, such values can be considered “wild.” After ...