You want to go to a club but to get in you must respond correctly to what the bouncer says. The bouncer says 12 to one man and the man responds 6, he is allowed in. The bouncer says 6 to another man and the man says 3, he too is allowed in. A third man walks up and the bouncer says 10 and the man responds 5, but he is denied entry.

What number should he have said to get in?