From the numbers 1, 2, 3, 4, 5, and 6, how many ways are there to choose two numbers so that their sum is not divisible by 3?
从1、2、3、4、5、6这些数中，任取两个数，使其和不能被3整除，则有多少种取法．
<gadget id="calculator">1 + 3 + 6</gadget>
<output>10</output>

<result>10</result>