Question 9
A wizard paints in grey four squares of an infinite grid table, as shown in the diagram below on the left. Then he casts a spell so that, at every second, each square that has at least one common side with those grey squares becomes also grey. For example, after 1 second, there will be 18 grey squares as shown in the diagram below on the right. What is the number of grey squares after 60 seconds?
