The standard positional numeral systems differ from one another only in the base they use.

This article summarizes facts on some non-standard positional numeral systems.

It is a Non-standard positional numeral systems which uses the imaginary number 2'i' as its base (mathematics).

The same trichotomy holds for other base-n positional numeral systems:

Compared to standard positional numeral systems, the unary system is inconvenient and is not used in practice for large calculations.

Mixed radix numeral systems are non-standard positional numeral systems in which the numerical base varies from position to position.

(In certain non-standard positional numeral systems, including bijective numeration, the definition of the base or the allowed digits deviates from the above.)

Non-standard positional numeral systems here designates numeral systems that may loosely be described as positional systems, but that do not comply with the following description of standard positional systems:

It is sometimes convenient to consider positional numeral systems where the weights associated with the positions do not form a geometric sequence 1, b, b, b, etc., starting from the least significant position, as given in the polynomial form.