There is a 6-story hollow phalanx with 25 people on each side of the outermost layer. How many students are needed to fill this hollow phalanx?
有一个6层的空心方阵，最外层每边25人，问要多少学生才能排出这个空心方阵？
<gadget id="calculator">25 - 6</gadget>
<output>19</output>

<gadget id="calculator">19 * 6 * 4</gadget>
<output>456</output>

<result>456</result>