Probability of collision

In yesterday's discussion of hash tables I asked how many cells do we need to randomly occupy in an array of size 1,000,000 before there is a 95% chance of collision. It turns out to be about 2440; i.e. the array only has to be 0.244% full! (See p18 of this week's slides, available online or via the CSSE Helpdesk, and the program circulated on the discussion list).