Imagine surrounding this ring with more cubes.
How many more cubes are needed now?
How many cubes will there be altogether?
Were you right?
What about a bigger ring? And another? And another?
How many cubes will there be in the 9th ring?
How many do you think there will be in the 100th ring?
How would you predict how many cubes there will be in any ring?
Thanks to Nrich for this problem.