Calculation: 1*2+2*5+3*8+4*11+...+20*59=how much.
计算：1*2+2*5+3*8+4*11+…+20*59=多少．
<gadget id="calculator">20 + 1</gadget>
<output>21</output>

<gadget id="calculator">2 * 20</gadget>
<output>40</output>

<gadget id="calculator">40 + 1</gadget>
<output>41</output>

<gadget id="calculator">41 / 6</gadget>
<output>41/6 = around 6.833333</output>

<gadget id="calculator">3 * 20 * 21 * (41/6)</gadget>
<output>8_610</output>

<gadget id="calculator">1 + 20</gadget>
<output>21</output>

<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">21 * 10</gadget>
<output>210</output>

<gadget id="calculator">8_610 - 210</gadget>
<output>8_400</output>

<result>8_400</result>