The Pythagoreans of ancient Greece were fascinated by whole numbers. One particular interest involved what we now call amicable numbers. Amicable numbers come in pairs in which each number is the sum ...

Here is last week's puzzle, as originally posted: Perfect numbers are numbers that equal the sum of their divisors. For example, the number 6 can be divided evenly by 1, 2, and 3, and 6 = 1 + 2 + 3.

The number 3120 is divisible without remainder by each number in the following set: 3, 312, 12, 120, 2 and 20. Each of these numbers will be called a visible proper divisor (VPD) of 3120 because ...