# 16. Appendix

*You really don’t know when to stop, do you?*

## 16.1. Basic algebra

Let’s introduce some number theory. Any number can be represented by the following term:

Now, that was very abstract. Let’s explain first, then make some examples.

The first thing you need to know is the numbers sign . It’s just a shorthand notation for a sum of many terms. The terms can use a sum variable which starts from an initial value and goes to some maximum value . So .

We also use two exponential laws, namely

Let’s make an example with base .

Let’s now write the same number in the binary system.

Since we’re dealing with computers, here’s an example with base . Let’s write the number 42 in binary.

## 16.2. Cryptography notes