The convention in math for writing numbers in bases larger than 10 is to insert capital letters after 9, starting with A. So, for example, the digits in base 12 are 0, 1, 2, …, 9, A, and B.
So if you’re familiar with math but not Linux, and you run across the base32 utility, you might naturally assume that the command converts numbers to base 32 using the symbols 0, 1, 2, &hellip, 9, A, B, C, …, V. That’s a reasonable guess, but it actually uses the symbols A, B, C, …, Z, 2, 3, 4, 5, 6, and 7. It’s all described in RFC 3548.
What’s going on? The purpose of base 32 encoding is to render binary data in a way that is human readable and capable of being processed by software that was originally written with human readable input in mind. The purpose is not to carry out mathematical operations.
Note that the digit 0 is not used, because it’s visually similar to the letter O. The digit 1 is also not used, perhaps because it looks like a lowercase l in some fonts.