(2/(1*3))+(3/(3*6))+(4/(6*10))+(5/(10*15))+(6/(15*21)).
(2/(1*3))+(3/(3*6))+(4/(6*10))+(5/(10*15))+(6/(15*21))．
<gadget id="calculator">1 * 3</gadget>
<output>3</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">3 * 6</gadget>
<output>18</output>

<gadget id="calculator">3 / 18</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">6 * 10</gadget>
<output>60</output>

<gadget id="calculator">4 / 60</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">10 * 15</gadget>
<output>150</output>

<gadget id="calculator">5 / 150</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">15 * 21</gadget>
<output>315</output>

<gadget id="calculator">6 / 315</gadget>
<output>2/105 = around 0.019048</output>

<gadget id="calculator">(2/3) + (1/6) + (1/15) + (1/30) + (2/105)</gadget>
<output>20/21 = around 0.952381</output>

<result>20/21 = around 0.952381</result>