Maths Puzzle - 18

A friend gave me this puzzle today.

A man wanted to enter a club

Every member knew the password,

The man hid himself beside a wall and tried to listen to the password.

A member came, watchman said 'twelve'

Member replied 6,

Watchman opened door.

Another member came, watchman said 'six'

Membr replied 3,

Watchman opened door.

Man thought he had got the password

He went to the door,

Watchman said 'eight'

Man replied 4. Watchman didn't open door.

What was the password?