Perfect (super) edge-magic crowns
  In this paper we continue the study of the valences for (super) edge-magic labelings of crowns $C_{m}\odot \overline K_{n}$ and we prove that the crowns are perfect (super) edge-magic when $m=pq$ where $p$ and $q$ are different odd primes. We also provide a lower bound for the number of different valences of $C_{m}\odot \overline K_{n}$, in terms of the prime factors of $m$. 
Susana-Clara L\'opez, Francesc-Antoni Muntaner-Batle and Mohan Prabu
math.CO