There are 7 layers of fruit trees planted equidistantly around a square pond, and 51 trees are planted on each side of the middle layer. How many trees are planted in this pond?
一块正方形池塘四周等距离栽了7层果树，中间一层每边栽了51棵，这个池塘共栽了多少棵树？
<gadget id="calculator">51 * 4</gadget>
<output>204</output>

<gadget id="calculator">204 - 4</gadget>
<output>200</output>

<gadget id="calculator">7 - 1</gadget>
<output>6</output>

<gadget id="calculator">6 * 8</gadget>
<output>48</output>

<gadget id="calculator">200 + 48</gadget>
<output>248</output>

<gadget id="calculator">248 + 4</gadget>
<output>252</output>

<gadget id="calculator">252 / 4</gadget>
<output>63</output>

<gadget id="calculator">63 - 7</gadget>
<output>56</output>

<gadget id="calculator">56 * 7 * 4</gadget>
<output>1_568</output>

<result>1_568</result>