A seven-digit number, each of which is 1, 2 or 3, and there are no consecutive two 1s, how many such seven-digit numbers are there?
一个七位数，每位都是1、2或者3，而且没有连续的两个1，这样的七位数一共有多少个．
<gadget id="calculator">2 ** 7</gadget>
<output>128</output>

<gadget id="calculator">7 ** 1</gadget>
<output>7</output>

<gadget id="calculator">2 ** 6</gadget>
<output>64</output>

<gadget id="calculator">7 * 64</gadget>
<output>448</output>

<gadget id="calculator">2 ** 3</gadget>
<output>8</output>

<gadget id="calculator">128 + 448 + 480 + 160 + 8</gadget>
<output>1_224</output>

<result>1_224</result>