2. 4, 7, 12, 21, 38, 71, (), 265 what do you fill in the brackets?

136 should be filled, and the analysis is as follows:
2*2-0=4
4*2-1=7
7*2-2=12
12*2-3=21
21*2-4=38
38*2-5=71
71*2-6=136
136*2-7=265

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