Find a general formula of the following sequence: 3 / 2, 5 / 4, 9 / 16, 17 / 256

Find a general formula of the following sequence: 3 / 2, 5 / 4, 9 / 16, 17 / 256

An = = (2 ^ n + 1) / (2 ^ N-1 of 2))
The denominator is a double exponential function
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