A perfect number is one whose proper factors add up to the number. For example, 6 = 1+2+3. What's the next "perfect number"?

Following the example of 6, the next number to achieve this unique mathematical balance is 28. To verify its "perfect" status, we simply need to find all of its proper factors, which are the numbers that can divide it evenly, excluding the number itself. The proper factors of 28 are 1, 2, 4, 7, and 14. Adding these divisors together (1 + 2 + 4 + 7 + 14) gives a sum of exactly 28, confirming its place in this special sequence.

The fascination with perfect numbers is ancient, dating back to the Greek mathematician Euclid more than two thousand years ago. He discovered a formula for generating these elusive numbers. The formula states that if (2^p - 1) is a prime number (what's now called a Mersenne prime), then the number 2^(p-1) * (2^p - 1) will be a perfect number. For 6, p=2, which gives 2 * 3. For 28, p=3, which gives 4 * 7.

Perfect numbers are incredibly rare. After 6 and 28, the next two are 496 and 8,128. To this day, only 51 perfect numbers have been discovered, and all of them are even. Whether an odd perfect number exists remains one of the oldest unsolved problems in all of mathematics, a testament to how much mystery can be hidden within simple arithmetic.