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{\bf Janine Bastian, Thomas Prellberg, Martin Rubey and Christian Stump}
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{\bf Counting the Number of Elements in the Mutation Classes of $\tilde A_n-$Quivers}
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In this article we prove explicit formulae for the number of
non-isomorphic cluster-tilted algebras of type $\tilde A_n$ in the
derived equivalence classes.  In particular, we obtain the number of
elements in the mutation classes of quivers of type $\tilde A_n$.  As a
by-product, this provides an alternative proof for the number of
quivers mutation equivalent to a quiver of Dynkin type $D_n$ which was
first determined by Buan and Torkildsen.

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