There is such a three-digit number, the number in the ones place is twice the number in the tens place, and the number in the hundreds place is larger than the number in the tens place but smaller than the number in the ones place. Ask how many such three-digit numbers there are.
有这样的三位数，它的个位上的数是十位上的数的2倍，百位上的数比十位上的数大而比个位上的数小．问共有多少个这样的三位数．
<gadget id="calculator">1 + 2 + 3</gadget>
<output>6</output>

<result>6</result>