Covering a 2*7 rectangle with 1*2 small squares, how many different covering methods are there?
用1*2的小方格覆盖2*7的长方形，共有多少种不同的覆盖方法？
<gadget id="calculator">1 + 4 + 10 + 6</gadget>
<output>21</output>

<result>21</result>