A number of students stand in a hollow three-layer square array. It is known that there are 23 people on each side of the outermost layer. How many students are there in this square array?
由若干名同学站成一个中空的三层方阵，已知最外层的每边上有23人，这个方阵中一共有多少名同学．
<gadget id="calculator">23 - 3</gadget>
<output>20</output>

<gadget id="calculator">20 * 3 * 4</gadget>
<output>240</output>

<result>240</result>