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I realised after posting that they were the same, but not when I was working through the mathematics.@Master1022 as I check again High School problem ##1 c## I see that you mean that the total sum is ##1## plus a new layer (=possible positions) each time and the series is on even numbers, so you finally mean ##(n + 1)^2## but the way is written is more cumbersome than it needs to. So, what is the difference from ##n## being odd?