This is a three star problem so hopefully it will keep students
thinking and testing their reasoning for some while.
Working systematically helps greatly. A table of results shows a
very clear pattern, and from there the challenge is to find a way
of accounting for that pattern.
This problem offers an excellent opportunity for reasoning from the
n case to the n + 1 case.
Seeing the n case result embedded within the n + 1 starting line
You may be interested to know that this problem was taken from the
book called Maths trails