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  2. Ternary numeral system - Wikipedia

    en.wikipedia.org/wiki/Ternary_numeral_system

    A ternary / ˈ t ɜːr n ər i / numeral system (also called base 3 or trinary [1]) has three as its base.Analogous to a bit, a ternary digit is a trit (trinary digit).One trit is equivalent to log 2 3 (about 1.58496) bits of information.

  3. Stack-sortable permutation - Wikipedia

    en.wikipedia.org/wiki/Stack-sortable_permutation

    The permutation graphs of stack-sortable permutations are trivially perfect. [4] For each element i of a permutation p, define b i to be the number of other elements that are to the left of and greater than i. Then p is stack-sortable if and only if, for all i, b i − b i + 1 ≤ 1. [1]

  4. Lehmer code - Wikipedia

    en.wikipedia.org/wiki/Lehmer_code

    The usual way to prove that there are n! different permutations of n objects is to observe that the first object can be chosen in n different ways, the next object in n − 1 different ways (because choosing the same number as the first is forbidden), the next in n − 2 different ways (because there are now 2 forbidden values), and so forth.

  5. Enumerative combinatorics - Wikipedia

    en.wikipedia.org/wiki/Enumerative_combinatorics

    Although counting the number of elements in a set is a rather broad mathematical problem, many of the problems that arise in applications have a relatively simple combinatorial description. The twelvefold way provides a unified framework for counting permutations, combinations and partitions.

  6. Steinhaus–Johnson–Trotter algorithm - Wikipedia

    en.wikipedia.org/wiki/Steinhaus–Johnson...

    The ! permutations of the numbers from 1 to may be placed in one-to-one correspondence with the ! numbers from 0 to ! by pairing each permutation with the sequence of numbers that count the number of positions in the permutation that are to the right of value and that contain a value less than (that is, the number of inversions for which is the ...

  7. Inclusion–exclusion principle - Wikipedia

    en.wikipedia.org/wiki/Inclusion–exclusion...

    The number of permutations satisfying the restrictions is thus: 4! − (12 + 6 + 0 + 0) + (4) = 24 − 18 + 4 = 10. The final 4 in this computation is the number of permutations having both properties P 1 and P 2. There are no other non-zero contributions to the formula.

  8. Complexity function - Wikipedia

    en.wikipedia.org/wiki/Complexity_function

    A balanced sequence is one for which the set of factors is balanced. [12] A balanced sequence has complexity function at most n+1. [13] A Sturmian word over a binary alphabet is one with complexity function n + 1. [14] A sequence is Sturmian if and only if it is balanced and aperiodic. [2] [15] An example is the Fibonacci word.

  9. Permutation pattern - Wikipedia

    en.wikipedia.org/wiki/Permutation_pattern

    In combinatorial mathematics and theoretical computer science, a (classical) permutation pattern is a sub-permutation of a longer permutation.Any permutation may be written in one-line notation as a sequence of entries representing the result of applying the permutation to the sequence 123...; for instance the sequence 213 represents the permutation on three elements that swaps elements 1 and 2.