Factorial 
an arbitrary integer 
is determined by the formula:
By definition, the factorial of 
Factorial 
equal to the number of permutations of elements.
In combinatorics , the factorial of a natural number is interpreted as the number of permutations (ordering) of the set with elements. For example, the set {A, B, C, D} of 4 elements there are 
changes:
Table factoral numbers from 1 to 25
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