Odd number sums give squares

Here's the answer to the question from last time...
前回の問題の答えはこちらです...

The sums add up to 1,4,9,16,25 etc, i.e. the squares 1x1, 2x2, 3x3, 4x4, 5x5, etc (this much was easy!)
合計は　１，４，９，１６，２５, ... になりますよね。　つまり、　数の二乗：　１x１，２x２，３ｘ３，４ｘ４，５ｘ５　とか　（ここまでは簡単だね！）

And the reason... we can see by arranging (for example) Japanese 1-yen coins in L-shapes, to make squares, as in the picture below.
で、その理由は... この絵で分かる。　一円玉を使って、L-形を作って、それで四角の形を作れるでしょう。