(1/(1*3))+(1/(3*5))+(1/(5*7))+(1/(7*9)).
(1/(1*3))+(1/(3*5))+(1/(5*7))+(1/(7*9))．
<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">7 * 9</gadget>
<output>63</output>

<gadget id="calculator">1 / 63</gadget>
<output>1/63 = around 0.015873</output>

<gadget id="calculator">(1/3) + (1/15) + (1/35) + (1/63)</gadget>
<output>4/9 = around 0.444444</output>

<result>4/9 = around 0.444444</result>