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I googled for this information but couldn't find anything...

What is the automorphism group of the additive group of the dyadic rationals $\mathbb{Z}[\frac{1}{2}]$ ?

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    It is its own endomorphism ring, so its automorphism group is just its group of units (acting by multiplication). $\langle -1 \rangle \times \langle 2 \rangle \cong C_2 \times C_\infty$2012-07-02
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    @JackSchmidt: Would you like to make that an answer?2012-07-02

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