How many numbers are there in the sequence 1, 3, 5, ..., 13?
数列1，3，5，…，13，共有多少个数．
<gadget id="calculator">13 - 1</gadget>
<output>12</output>

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">6 + 1</gadget>
<output>7</output>

<result>7</result>