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Permutations ➡
The factorial function Permutations Combinations Problem solving with permutations and combinations

Permutations and combinations — The factorial function

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📘 Notes

The Factorial Function

Factorials are used to count arrangements and selections in probability and combinatorics.

1. Definition

For any positive integer \(n\):

\[ n! = n(n-1)(n-2)\dots 3\times2\times1 \]

Special case:

\[ 0! = 1 \]

2. Examples

\[ 5! = 5\times4\times3\times2\times1 = 120 \] \[ 4! = 24 \] \[ 3! = 6 \]
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