Quaternary

Quaternary (also known as Quadral or base 4) is a positional number system structured around the number 4 and its powers. It is the smallest composite base.

Usage
Despite being the first composite base, quaternary usage is largely limited. While it can be used as a compact representation of binary, quaternary is still a part of the lower natural scale, meaning that it has low digit diversity and its numbers rise to large sizes very fast. However, as is the case with most bases in this scale, most of its usage comes from an object having four possible states, or the ability for something to have 4 different values. A notable use of quaternary is in DNA and RNA. It is a "chemical base-4 system" encoding adenine, guanine, cytosine and thymine (or uracil in RNA).

Irrational numbers
Here are the most commonly used irrational numbers expressed in quaternary:

Multiplication table
The quaternary multiplication table is simple and contains 3 non-trivial products: 2*2=10, 2*3=12 and 3*3=21.

Exponentiation table
As quaternary is a prime power base, the powers of 2 are very easy to remember:

Fractions table
As quaternary is a prime power base, only fractions with denominators that are powers of that prime will terminate.

Related number systems

 * Binary digits correspond to 1/2 of a quaternary digit - each quaternary digit can be written as two binary digits.
 * Hexadecimal digits correspond to 2 quaternary digits.
 * Tetrasexagesimal digits correspond to 3 quaternary digits.
 * Base 256 digits correspond to 4 quaternary digits.
 * Negaquaternary is the negative base corresponding to quaternary.
 * Bijective quaternary is the bijective base corresponding to quaternary.
 * Skew quaternary is the skew base corresponding to quaternary.
 * Balanced quaternary is the balanced base corresponding to quaternary, although as an even balanced base it is not well defined.