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There are only two non-Abelian groups of order eight.
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One of these is the Quaternion group.
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The dihedral group of order (and degree ) is the other group of order . It is not isomorphic to the quaternion group.
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However, the quaternion and dihedral groups of order eight do have the same character tables.
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(Notice, however, that the quaternion group has a single conjugacy class of involutions, while the dihedral group of order has three conjugacy classes of involutions.)
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The quaternion group is an example of a Hamiltonian group - every one of its subgroups is normal. This is evident from the subgroup lattice diagram above; alternatively, Hamiltonicity can be demonstrated, as follows.
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Like the dihedral group of order , the quaternion group is an extra-special -group.
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The quaternion group of order is Hamiltonian, but generalized quaternion groups of larger order are not.
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Quaternion groups do not have perfect order classes.
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