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 ...

The crisp new dollar bill that I have just taken from my wallet bears the serial number 24598176. It’s easy to tell that the number is exactly divisible by 2 but not by 5. Is it divisible by 3? by 4?

WITH respect to Mr. Burgess's letter in your issue of November 4, perhaps the following general rule for testing the divisibility of a given number by another, which I found some days ago, may be of ...