From the seven numbers 1, 2, 3, 4, 5, 6, and 7, choose three numbers so that their sum can be divisible by 3. How many different ways are there to choose?
从1，2，3，4，5，6，7这七个数中，选取三个数使它们的和能被3整除，那么不同的选法有多少种？
<gadget id="calculator">2 + 3 + 5 + 3</gadget>
<output>13</output>

<result>13</result>