# Permutations

Definition: Combinatorics is a branch of mathematics about the selection and deployment of elements of a set based on some conditions

Selected (or available) group of elements called compounds

## Permutations

Definition: Permutations of the different elements are called finite ordered set (that is, such sets that specify the order of elements) can be removed from a set containing elements (if all elements of a given set of different — get permutations without repetitions, but if in the given set elements may be repeated, then get the permutations with repetitions)

### Formula for the number of permutations

#### Without repetition

For (by definition)

Example. The number of different six-digit numbers can be formed from the digits without repeating the numbers in one number equal to

#### With repetitions

where

Example.The number of different six-digit numbers can be formed from three twos, two sevens and one five

(considered )

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Chapter: Combinatorics
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