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# Permutations

A permutation involves rearranging the elements of a set in a situation where order is important. For example, there are 6 ways to permute the set $$\{ 1, 2, 3 \}$$: $$(1,2,3), (1,3,2), (2, 1, 3), (2,3,1), (3,1,2), (3,2,1)$$.

In general, there are $$n! = 1 \times 2 \times 3 \times \dots \times n$$ ways to permute a set of $$n$$ elements, and $$\frac{n!}{(n-k)!}$$ ways to permute $$k$$ elements of an $$n$$-sized set.

Note by Arron Kau
2 years, 11 months ago