Select the number from among the given options that can replace the question mark (?) in the following series.
6, 11, 21, 41, 81, ?
$$6\times2-1 = 12-1 = 11$$
$$11\times2-1 = 22-1 = 21$$
$$21\times2-1 = 42-1 = 41$$
$$41\times2-1 = 82-1 = 81$$
$$81\times2-1 = 162-1 = 161$$
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