Use one or more of the five weights of 1 gram, 3 gram, 9 gram, 27 gram and 81 gram, and put them on one end of the balance to weigh the object. A total of 31 weights can be weighed, and they are arranged from small to large It is: 1 gram, 3 grams, 4 grams, 9 grams, 10 grams, 12 grams... How much is the 30th weight in grams?
用1克、3克、9克、27克、81克五个砝码中的一个或几个，放在天平的一端称物体的重量，一共可以称出31个重量，把它们从小到大排列起来是：1克、3克、4克、9克、10克、12克…第30个重量是多少克．
<gadget id="calculator">3 + 9 + 27 + 81</gadget>
<output>120</output>

<result>120</result>