A series of numbers arranged according to the law: 1, 2, 4, 7, 11, 16, 22, 29, ... What is the 15th number in this series of numbers.
按规律排列的一串数：1，2，4，7，11，16，22，29，…这串数中第15个数是多少．
<gadget id="calculator">1 + 15</gadget>
<output>16</output>

<gadget id="calculator">16 * 7</gadget>
<output>112</output>

<gadget id="calculator">1 + 112 + 8</gadget>
<output>121</output>

<result>121</result>