What is the next number in the sequence.
15 29 56 108 208 ?  Choices:
A) 450
B) 400
C) 300
D) 500
E) 580
400   400   Explanation:   400egins with 15   2*15-1= 
<gadget id="calculator">2*15-1</gadget>
<output>29</output>
&gt; 29   2*29-2= 
<gadget id="calculator">2*29-2</gadget>
<output>56</output>
&gt; 56   2*56-4= 
<gadget id="calculator">2*56-4</gadget>
<output>108</output>
&gt; 108   2*108-8= 
<gadget id="calculator">2*108-8</gadget>
<output>208</output>
&gt; 208   2*208-16= 
<gadget id="calculator">2*208-16</gadget>
<output>400</output>
&gt; 400
<result>B</result>
What is the next number in the sequence.
15 29 56 108 208 ?