MathCastle
ChallengeMediumInclusion–Exclusion, Derangements & Pigeonhole

Inclusion--Exclusion, Derangements & Pigeonhole · Medium problem

How many permutations of (1,2,3,4,5,6)(1,2,3,4,5,6) have exactly two values fixed (i.e. exactly two indices ii with the ii-th entry equal to ii)?