Fill in the appropriate numbers in the brackets according to certain rules: 2, 1, 3, 4, 7, how much, 18, 29, 47.
按一定的规律在括号中填上适当的数：2，1，3，4，7，多少，18，29，47．
<gadget id="calculator">4 + 7</gadget>
<output>11</output>

<result>11</result>