How many different three-digit numbers can be dialed out in total by using 6 beads to dial out three-digit numbers on the counter?
用6个算珠在计数器上拨出三位数，一共可以拨出多少种不同的三位数．
<gadget id="calculator">1 + 2 + 3 + 4 + 5 + 6</gadget>
<output>21</output>

<result>21</result>