A permutation is an arrangement of objects in a particular order. For example, the permutations of the letters "ABC" would be "ABC," "ACB," "BAC," "BCA," "CAB," and "CBA." The number of permutations of a set of objects is given by the factorial of the number of objects. For example, the number of permutations of 4 objects would be 4! = 4 x 3 x 2 x 1 = 24.
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