15
$\begingroup$

Give a combinatorial argument to prove that the number of derangements satisfies the following relation:

$$d_n = (n āˆ’ 1)(d_{nāˆ’1} + d_{nāˆ’2})$$

for $n \geq 2$.

I am able to prove this algebraically but not able to see the combinatorial example.

  • 2
    This is possibly a duplicate of [this question](http://math.stackexchange.com/questions/83380). – 2012-09-28

3 Answers 3