How many simple fractions have the denominator 72?
分母是72的最简真分数共有多少个．
<gadget id="calculator">72 / 2</gadget>
<output>36</output>

<gadget id="calculator">36 - 1</gadget>
<output>35</output>

<gadget id="calculator">72 / 3</gadget>
<output>24</output>

<gadget id="calculator">24 - 1</gadget>
<output>23</output>

<gadget id="calculator">71 - 35 - 23</gadget>
<output>13</output>

<gadget id="calculator">72 / 6</gadget>
<output>12</output>

<gadget id="calculator">12 - 1</gadget>
<output>11</output>

<gadget id="calculator">13 + 11</gadget>
<output>24</output>

<result>24</result>