(1/(1*3))+(1/(3*5))+(1/(5*7))+(1/(17*19))+(1/(19*21)).
(1/(1*3))+(1/(3*5))+(1/(5*7))+(1/(17*19))+(1/(19*21))．
<gadget id="calculator">1 * 3</gadget>
<output>3</output>

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

<gadget id="calculator">3 * 5</gadget>
<output>15</output>

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

<gadget id="calculator">5 * 7</gadget>
<output>35</output>

<gadget id="calculator">1 / 35</gadget>
<output>1/35 = around 0.028571</output>

<gadget id="calculator">17 * 19</gadget>
<output>323</output>

<gadget id="calculator">1 / 323</gadget>
<output>1/323 = around 0.003096</output>

<gadget id="calculator">19 * 21</gadget>
<output>399</output>

<gadget id="calculator">1 / 399</gadget>
<output>1/399 = around 0.002506</output>

<gadget id="calculator">(1/3) + (1/15) + (1/35) + (1/323) + (1/399)</gadget>
<output>155/357 = around 0.434174</output>

<result>155/357 = around 0.434174</result>