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For Charlie's Squares

To work out the coordinate of the midpoint of any squares on the graph you can use the formula:
(2+3(n-1),2+1(n-1)). To get to the next midpoint you have to add 3 on the x axis and 1 on the y axis.
n = any number as long as you take the first square back from the first in Charlie's graph. n=1 is charlie's first square. n=0 is charlie's first square back.
This strategy works for going backward as well as forward.

Using this you can work out that square 3 is (8,4) and 20 is (59,21).