An activity for mental part of lesson called "The Disappearing Man":

Draw an outline of a man on the whiteboard with trousers, shirt, shoes e.t.c. In the spaces write the numbers that your topic is focused on e.g. prime numbers, multiples of 13, factors of 40...

Children come to the board and erase a number explaining why it has been rubbed out until all of the figure has disappeared. Figures could include hats, scarves, football shirts, be kicking a ball (also with a number inside), be male or female e.t.c.

A completely flexible way of practicing number properties.