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Writing functions:

arrangement(n, k)

In combinatorics placement referred to as the location of the objects on some «places» provided that every place is occupied by exactly one object and all the objects are different. More formally, the placement (n-k) is called an ordered set of k different elements of some n-element set.


One of the most important areas of mathematics is combinatorics, which studies combinatorial objects and their properties. In the framework of combinatorics, the placement of elements is one of the fundamental operations.

The placement of elements is a process of orderly selection and arrangement of elements from a certain set. Unlike permutations, placement takes into account the order of the selected elements. It is assumed that all the elements are different.

To mathematically describe the placement of elements, a function is used that takes two arguments: the set from which the elements are selected, and the number of elements to be placed. Let's denote these arguments as n and k, respectively.

The element placement function is usually denoted as A(n, k). Its value is equal to the number of ways in which k elements can be selected and placed in an orderly manner from a set of n elements. The formula for calculating the placement function is written as follows:

A(n, k) = n! / (n - k)!

where n is! denotes the factorial of the number n, that is, the product of all natural numbers from 1 to n.

This function is an important tool for solving various combinatorics problems, such as calculating the number of subsets, distributing places in a circle, and many others.

So, the element placement function allows us to determine the number of ways in which k elements can be selected and placed in an orderly manner from a given set of n elements. It is an important tool for studying combinatorics and solving a variety of problems that we face both in mathematics and in other fields of science and technology.