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A permutation without repetition of all elements from set of n elements is ordered sequence of all distinct elements from this set. The number of permutations is given by formula P_n = n!. Examples. Permutation without repetition of 2 elements a, b: ab, ba. P_2 = 2! = 1⋅2 = 2. Permutation without repetition of 3 elements a, b, c: abc, acb, bac, bca, cab, cba. P_3 = 3! = 1⋅2⋅3 = 6. Permutation without repetition of 4 elements a, b, c, d: abcd, abds, acdb, adbc, adcb, bacd, badc, bcad, bcda, bdac, bdca, cabd, cadb, cbad, cbda, cdab, cdba, dabc, dacb, cbac, dbca, dcab, dcba. P_4 = 4! = 1⋅2⋅3⋅4 = 24.