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Abstract Algebra

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Moderate

Cyclicity of U(20)

ABSALG-VLDTGL

Which of the following is the group $U(20)$ of units of $\mathbb{Z}_{20}$ isomorphic to?

A

$\mathbb{Z}_{8}$

B

$\mathbb{Z}_2\times\mathbb{Z}_{4}$

C

$\mathbb{Z}_2\times\mathbb{Z}_2\times\mathbb{Z}_2$

D

$\mathbb{Z}_5\times\mathbb{Z}_4$

E

None of the above