It’s easy to tell if a given whole number is divisible by 2. Just check whether the last digit is even. There are also simple rules to determine whether a number is ...

You probably haven’t had to do longhand math in years, but you do mental math every day. Or maybe you google math problems ten times a day, because you’ve forgotten how to do any math beyond your ...

This article is a modified and updated version of one I wrote in—oddly enough—2008 and then updated for 2012. Barring a colossal asteroid impact or a Trump presidency, I’ll probably be around to do it ...

Learn how to check divisibility by 13 with Sall's Theorem! This easy-to-follow method helps you determine if a number is divisible by 13 without doing long division. Perfect for math enthusiasts and ...