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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.
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]
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 × ...
In practice, the radix complement is more easily obtained by adding 1 to the diminished radix complement, which is (). While this seems equally difficult to calculate as the radix complement, it is actually simpler since ( b n − 1 ) {\displaystyle \left(b^{n}-1\right)} is simply the digit b − 1 {\displaystyle b-1} repeated n {\displaystyle ...
The positional systems are classified by their base or radix, which is the number of symbols called digits used by the system. In base 10, ten different digits 0, ..., 9 are used and the position of a digit is used to signify the power of ten that the digit is to be multiplied with, as in 304 = 3×100 + 0×10 + 4×1 or more precisely 3×10 2 ...
The generalization to radix representations, for >, and to =, is a digit-reversal permutation, in which the base-digits of the index of each element are reversed to obtain the permuted index. The same idea can also been generalized to mixed radix number systems. In such cases, the digit-reversal permutation should simultaneously reverses the ...
For calendrical use, the Mayan numeral system was a mixed-radix system, since one of its positions represents a multiplication by 18 rather than 20, in order to fit a 360-day calendar. Also, giving an angle in degrees, minutes and seconds (with decimals), or a time in days, hours, minutes and seconds, can be interpreted as mixed-radix systems.
Converting successive natural numbers to the factorial number system produces those sequences in lexicographic order (as is the case with any mixed radix number system), and further converting them to permutations preserves the lexicographic ordering, provided the Lehmer code interpretation is used (using inversion tables, one gets a different ...