Ordering
The number of "arrangements" in an ordering of n items is given by either a combination (order is ignored) or a permutation (order is significant).
An ordering (or order) is also a method for choosing the order in which elements are placed (i.e., a sorting function).
The Wolfram Language function Ordering [p] gives the inverse permutation of a given permutation p.
See also
Arrangement, Combination, Cutting, Derangement, Inverse Permutation, Lexicographic Order, Monomial Order, Ordering Axioms, Partial Order, Permutation, Sorting, Total Order, Transposition Order, Well Ordered SetExplore with Wolfram|Alpha
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Cite this as:
Weisstein, Eric W. "Ordering." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/Ordering.html