For a square chessboard, if the outermost layer is filled with 40 chess pieces, how many pieces are needed if the interior is completely filled?
一正方形棋盘，最外层摆满需40个棋子，则内部全部摆满，共需多少棋子？
<gadget id="calculator">40 / 4</gadget>
<output>10</output>

<gadget id="calculator">10 + 1</gadget>
<output>11</output>

<gadget id="calculator">11 * 11</gadget>
<output>121</output>

<result>121</result>