Calculation: (2/21)+(2/77)+(2/165)+...+(2/1677).
计算：(2/21)+(2/77)+(2/165)+…+(2/1677)．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 / 43</gadget>
<output>1/43 = around 0.023256</output>

<gadget id="calculator">(1/3) - (1/43)</gadget>
<output>40/129 = around 0.310078</output>

<gadget id="calculator">(1/2) * (40/129)</gadget>
<output>20/129 = around 0.155039</output>

<result>20/129 = around 0.155039</result>