Combinatorics and Graph Theory · Problem 2.2.7

Inclusion-Exclusion — David Guichard

Mathematics — Combinatorics · derangements-combinatorial-proof

Problem

Give a combinatorial proof that n!=∑k=0n(nk)Dn−k.n! = \sum_{k=0}^{n} \binom{n}{k} D_{n-k}.

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