retired worker from Nantong Lighting Factory specially made a seven-story pagoda called Oriental Famous Pearl to welcome the Shanghai World Expo. There are 381 colored lights in total. It is twice that of the upper floor. How many lamps are installed on the top floor of the tower?
南通灯具厂的一位退休工人为迎接上海世博会的召开特地制作了一盏名为东方名珠的七层宝塔，共用彩灯381盏，从塔顶向下，每下一层灯的盏数都是上一层的2倍，问塔的顶层装几盏灯？
<gadget id="calculator">1 + 2 + 4 + 8 + 16 + 32 + 64</gadget>
<output>127</output>

<gadget id="calculator">381 / 127</gadget>
<output>3</output>

<result>3</result>