From the nine numbers 1 to 9, any odd number is multiplied by an even number. How many different products are there?
1至9这九个数中任取一个奇数和一个偶数相乘，不同的乘积有多少个．
<gadget id="calculator">1 * 6</gadget>
<output>6</output>

<gadget id="calculator">3 * 6</gadget>
<output>18</output>

<result>18</result>