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Nice: find number of even permutations with no fixed points

Source: Moldova 2008 IMO-BMO Second TST Problem 4

March 29, 2008
countingderangementinductionlinear algebracombinatorics proposedcombinatorics

Problem Statement

Find the number of even permutations of {1,2,…,n} \{1,2,\ldots,n\} with no fixed points.
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