How many square centimeters of cardboard is needed to make a cube without a lid, and the side length is 21 centimeters?
做一个正方体无盖纸盒，棱长是21厘米，至少需要多少平方厘米的纸板？
<gadget id="calculator">21 * 21 * 5</gadget>
<output>2_205</output>

<result>2_205</result>