**28** is a perfect number. In mathematics, a *perfect number* is a number that is equal to the sum of all of its factors. Think back to your arithmetic days: what are the factors of **28**?

1, 2, 4, 7, 14

That’s right. And if you add them all together?

1 + 2 + 4 + 7 + 14 = **28**

Very few numbers have this property. Ancient Greek mathematician Euclid knew about the first four: 6, **28**, 496, and 8128. It wasn’t until the Middle Ages that the next one was discovered: 33,550,336. And from that point, they just keep getting bigger and bigger. So far, 51 perfect numbers have been discovered; the highest one has over 49 million digits in it. I can’t imagine just how much time it took a computer to crunch numbers to get to that. Or how much time it took to program said computer. (Which is a better use of computer time? Working that out, or watching cat videos on Facebook? I’m honestly not sure.)

I recently learned that **28** also has some other cool properties. Check this out. Do you remember *prime numbers*? They’re numbers which have only two factors: themselves and 1. Numbers like 7 and 11. There’s no whole number that can evenly divide into either 7. (Except 7 itself, and 1.) Numbers that are not prime are called *composite numbers*. Numbers like 6 and 12. Six is 2 x 3. Twelve is 2 x 6 or 3 x 4. Composite numbers have more factors than just themselves and 1. Okay, now here’s the cool thing. Add up the first five *prime numbers.*

2 + 3 + 5 + 7 + 11 = **28**

Now add up the first five *non-prime numbers*. (We include 1, because it’s not prime, although it’s not exactly composite either.)

1 + 4 + 6 + 8 + 9 = **28**

That’s cool. The first five primes and the first five non-primes add up to **28. **Is there a reason for that? Like a fundamental axiom of mathematics that makes this obvious? I don’t know. Does it mean that **28 **is some sort of divine number? Probably not. But I’ve always enjoyed math trivia like this. It’s like **28** is the special “adding number.” Add whatever you want together — at some point, it will equal **28.**

Including all the whole numbers themselves. Check this out:

1 + 2 + 3 + 4 + 5 + 6 + 7 = **28**

This is getting kind of creepy, actually. I’m not hanging out with **28** anymore. This number is like some kind of snake, you know… *ahem* … an adder?

I’ll get my coat.

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## Published by michael j scholtes

I am a time-worn preacher with no intent of malice.
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I love these blogs. Keep it up.

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