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The most familiar example of mixed-radix systems is in timekeeping and calendars. Western time radices include, both cardinally and ordinally, decimal years, decades, and centuries, septenary for days in a week, duodecimal months in a year, bases 28–31 for days within a month, as well as base 52 for weeks in a year.
"A base is a natural number B whose powers (B multiplied by itself some number of times) are specially designated within a numerical system." [1]: 38 The term is not equivalent to radix, as it applies to all numerical notation systems (not just positional ones with a radix) and most systems of spoken numbers. [1]
General mixed radix systems were studied by Georg Cantor. [2] The term "factorial number system" is used by Knuth, [3] while the French equivalent "numération factorielle" was first used in 1888. [4] The term "factoradic", which is a portmanteau of factorial and mixed radix, appears to be of more recent date. [5]
More general is using a mixed radix notation (here written little-endian) like for + +, etc. This is used in Punycode , one aspect of which is the representation of a sequence of non-negative integers of arbitrary size in the form of a sequence without delimiters, of "digits" from a collection of 36: a–z and 0–9, representing 0–25 and 26 ...
In contrast to decimal, or radix 10, which has a ones' place, tens' place, hundreds' place, and so on, radix b would have a ones' place, then a b 1 s' place, a b 2 s' place, etc. [2] For example, if b = 12, a string of digits such as 59A (where the letter "A" represents the value of ten) would represent the value 5 × 12 2 + 9 × 12 1 + 10 × ...
For example, 100 in decimal has three digits, so its cost of representation is 10×3 = 30, while its binary representation has seven digits (1100100 2), so the analogous calculation gives 2×7 = 14. Likewise, in base 3 its representation has five digits (10201 3 ), for a value of 3×5 = 15, and in base 36 (2S 36 ) one finds 36×2 = 72.
Examples of such numbers are shown in the right column of the table. All of them are repeating fractions with the repetend marked by a horizontal line above it. If the set of digits is minimal, the set of such numbers has a measure of 0. This is the case with all the mentioned coding systems.
The base e is the most economical choice of radix β > 1, [4] where the radix economy is measured as the product of the radix and the length of the string of symbols needed to express a given range of values. A binary number uses only two different digits, but it needs a lot of digits for representing a number; base 10 writes shorter numbers ...