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Abstract

We prove that for any automorphism $\phi$ of the restricted wreath product
$\mathbb{Z}_2 \mathrm{wr} \mathbb{Z}^k$ and $\mathbb{Z}_3 \mathrm{wr}
\mathbb{Z}^{2d}$ the Reidemeister number $R(\phi)$ is infinite, i.e. these groups have the property $R_\infty$. For $\mathbb{Z}_3 \mathrm{wr} \mathbb{Z}^{2d+1}$ and $\mathbb{Z}_p \mathrm{wr} \mathbb{Z}^k$, where $p>3$ is prime, we give examples of
automorphisms with finite Reidemeister numbers. So these groups do not have the
property $R_\infty$. For these groups and $\mathbb{Z}_m \mathrm{wr} \mathbb{Z}$, where $m$ is relatively prime to $6$, we prove the twisted Burnside-Frobenius theorem
(TBFT$_f$): if $R(\phi)<\infty$, then it is equal to the number of equivalence classes of finite-dimensional irreducible unitary representations fixed by the action $[\rho]\mapsto [\rho\circ\phi]$.