This video asks a question in simple combinatorics and works towards the answer, deriving a recursion relation for the number of ways to order n soldiers, when none is allowed to go in their correct position. The recursion relation is
D(n) = (n-1)(D(n-1) + D(n-2))
To explore this problem beyond the simple recursion relation, see my related blog post:
http://arcsecond.wordpress.com/2009/09/22/the-deranged-rockettes/
nice, i think you're missing some brackets though
Torontostringer 2 years ago