4 sticks are needed to place 1 square, 7 sticks are needed to place 2 squares, 10 sticks are needed to place 3 squares, how many sticks are needed to place n squares.
摆1个正方形需要4根小棒，摆2个需要7根小棒，摆3个需要10根小棒，摆n个正方形需要多少根小棒．
<gadget id="calculator">1 * 3</gadget>
<output>3</output>

<gadget id="calculator">1 + 3</gadget>
<output>4</output>

<result>4</result>