I recently misread an easy recreational puzzle as 'Into how many regions can six planes divide space?'.
It took me about half an hour to get an answer. (Which was the correct answer to the wrong question, but sadly the wrong answer to the right question). But it turned out to be great fun to think about.
1,2,4,8,..... how does this sequence continue?
So far Tim and Sips and Paul Cook have had a go. Paul guessed the answer but didn't know why it was true and I haven't heard anything from the other two.
Have fun! It's not actually that hard.