The fifth-grade students of Hongxing Primary School are arranged in a three-layer hollow square for military training, and there are 20 students on each side of the outermost layer, so how many students are there in total in this three-layer hollow square.
红星小学五年级学生军训，排成一个三层空心方阵，最外层每边有20名学生，那么这个三层空心方阵共有学生多少人．
<gadget id="calculator">20 - 3</gadget>
<output>17</output>

<gadget id="calculator">17 * 3 * 4</gadget>
<output>204</output>

<result>204</result>